The post-discrimination gradient as a function of discrimination training on a line-tilt continuum.

University of Windsor University of Windsor

Scholarship at UWindsor

Scholarship at UWindsor

Electronic Theses and Dissertations Theses, Dissertations, and Major Papers

1-1-1970

The post-discrimination gradient as a function of discrimination

The post-discrimination gradient as a function of discrimination

training on a line-tilt continuum.

training on a line-tilt continuum.

Laurence B. Gray

University of Windsor

Follow this and additional works at: https://scholar.uwindsor.ca/etd

Recommended Citation Recommended Citation

Gray, Laurence B., "The post-discrimination gradient as a function of discrimination training on a line-tilt continuum." (1970). Electronic Theses and Dissertations. 6853.

https://scholar.uwindsor.ca/etd/6853

This online database contains the full-text of PhD dissertations and Masters’ theses of University of Windsor students from 1954 forward. These documents are made available for personal study and research purposes only, in accordance with the Canadian Copyright Act and the Creative Commons license—CC BY-NC-ND (Attribution, Non-Commercial, No Derivative Works). Under this license, works must always be attributed to the copyright holder (original author), cannot be used for any commercial purposes, and may not be altered. Any other use would require the permission of the copyright holder. Students may inquire about withdrawing their dissertation and/or thesis from this database. For additional inquiries, please contact the repository administrator via email

THE POST-DISCRIMINATION GRADIENT AS A

FUNCTION OF DISCRIMINATION TRAINING ON

A LINE-TILT CONTINUUM

by

LAURENCE B. GRAY

B.A., University of Windsor, 1969

A Thesis

Submitted to the Faculty of Graduate Studies through the Department of Psychology in Partial Fulfillment

of the Requirements for the Degree of Master of Arts at

University of Windsor

UMI Number: EC52799

INFORMATION TO USERS

The quality of this reproduction is dependent upon the quality of the copy

submitted. Broken or indistinct print, colored or poor quality illustrations and

photographs, print bleed-through, substandard margins, and improper

alignment can adversely affect reproduction.

In the unlikely event that the author did not send a complete manuscript

and there are missing pages, these will be noted. Also, if unauthorized

copyright material had to be removed, a note will indicate the deletion.

®

UMI

UMI Microform EC52799

Copyright 2008 by ProQuest LLC.

All rights reserved. This microform edition is protected against

unauthorized copying under Title 17, United States Code.

ProQuest LLC 789 E. Eisenhower Parkway

PO Box 1346 Ann Arbor, Ml 48106-1346

ABSTRACT

Following preliminary and S+ only training, three groups of

pigeons were trained to discriminate between line-tilts of 0°

vertical (S+) and 30°, 45°, or 60° to the right of vertical respectively.

A control group, following a post«S+ only training generalization

test, was trained to discriminate between S+ and a lighted key with no

line. All Ss were then extinguished to 12 line orientations. While

behavioral contrast was observed, no experimental S showed a peak shift

in the post-discrimination generalization gradient. These results

were interpreted as providing some evidence to render questionable

the validity of generalizing from peak shift results obtained using the

dimension of wavelength to the dimension of angularity since the

results Suggest that the peak shift is not always obtained using line

tilt as the stimulus dimension.

PREFACE

The author wishes to express his gratitude and appreciation

to Dr, Theodore Hirota under whose direction the present research was

conducted. His willingness to give of his time and knowledge made

the carrying out of the research much less burdensome than it might

have been. Grateful appreciation is also extended to Drs. Arthur

Smith and Theodore Horvath for their help and constructive criticism

which they made available to the author throughout the course of the

experiment.

TABLE OF CONTENTS

Page

PREFACE . . . ... iii

LIST OF TABLES . ... v

LIST OF FIGURES . ... vi

Chapter I INTRODUCTION . . . ... 1

Background of Related Research ... . 1

Purpose of Present Research . . . 8

II METHOD ... 10

Subjects . . . 10

Apparatus . . . ... . . . . 10

Procedure . . . 11

III RESULTS . . . ... . . . 13

S+ Only Training ... 13

Discrimination Training . . 13

Generalization Test ... 13

IV DISCUSSION ... 32

V S U M M A R Y ... 36

APPENDIX A Order of Presentation of S+ and S-During Discrimination Training . . . 38

APPENDIX B Order of Presentation of Stimuli During Generalization Test . . . 39

APPENDIX C Responses During S+ Only Training . . . 40

APPENDIX D Responses During Discrimination Training . . . . 41

APPENDIX E Responses During Generalization Test . . . 43

REFERENCES ... . . . . 48

VITA AUCTORIS ... 51

iv

LIST OF TABLES

Table Page

1 Analysis of Variance of the Means of the

Generalization Gradients by Treatment

Groups . . . 15

2 Newman-Keuls Comparisons of Means of the

Generalization Gradients . . . 16

3 Analysis of Variance of the Means of

Total Responses During Generalization

by Treatment Groups ... 18

4 Analysis of Variance of Means of Total

Responses to the Modal Stimulus of the Generalization Gradient by Treatment

Groups . . . ... 19

LIST OF FIGURES

Figure Page

la, b, c, d Mean Response Rates During S+

Only Training . . . 20

2a, b, c, d Mean Response Rates as a Function

Discrimination Training . . . 24

3a, b, c, d Mean Post-Discrimination Gradients . . . 28

vi

CHAPTER I

INTRODUCTION

The purpose of the present study was to replicate Hanson's

(1959) peak shift (PS) results using line-tilt as the stimulus

dimension. The PS has been defined by Bloomfield (1967) as a:

displacement of the maximum point of the generalization gradient from the reinforcement correlated stimulus (S+) in a direction away from the negative, extinction

correlated stimulus (S-) after discrimination training.

The significance of such a study is perhaps more suitably discussed

in the light of some general background information concerning the

phenomenon of the PS and some of the relevant variables.

Background of Related Research

In a study of the effects of discrimination training on the

stimulus generalization gradient, Hanson (1959) demonstrated that under

certain conditions the peak of the post-discrimination gradient (PDG)

shifts away from the conditioned stimulus. He also demonstrated that

the slope of the PDG correlated with S- would be steeper than that

correlated with S+, resulting in an area shift in the PDG away from

S+ in a direction away from S-.

U s i n g pigeons, H a n s o n t r a i n e d fou r g r o u p s of Ss to d i s c r i m i n a t e

between 550 mji (S+) and 555, 560, 570, or 590 mp (S-). He then tested

for generalization to 13 stimuli, including the training S+ and S-

(except for the 555 mp group). Using Spence's (1937) model, Hanson

made six specific predictions with regard to the PDG:

a) The post-discrimination gradient will be steeper than the

generalization gradient in the region of S-.

b) If a complete discrimination is developed the value of the

post-discrimination gradient will be zero at S-.

c) The mode of the post-discrimination gradient will be

displaced away from S- in relation to the mode of the

generalization gradient.

d) The magnitude of this displacement will increase as the

S+, S- difference is reduced.

e) The maximum heights of the post-discrimination gradients

will be reduced as the S+, S- difference is reduced.

The first three predictions were clearly supported by the results

(although the second prediction appears to be a tautology since a

complete discrimination implies, by definition, no responding). All

but three of the 24 experimental_Ss showed a PS in the PDG. Hanson

claimed that the fourth prediction, that the magnitude of the modal

displacement increases as the S+, S- difference decreases, was also

supported. However, an examination of the mean generalization

gradients for the discrimination groups reveals that the mode of each

gradient was at the 540 mji stimulus. Thus, the amount of modal

d i s p l a c e m e n t in t h e P D G s w i t h r e s p e c t to the m o d e o£ th e control

gradient was the same for all groups. The last two predictions were

not confirmed by the results.

Other experimenters have demonstrated this PS effect: Honig,

Thomas & Guttman (1959); Honig (1962); Terrace (1964, 1966);

Friedman and Guttman (1965); Yarczower, Dickson & Gollub (1966);

Stevenson (1966); and Thomas and Burr (1969). All the above studies

used wavelength generalization in pigeons to demonstrate the PS

effect. Citing the failure of Jenkins and Harrison (I960) to demonstrate

the PS using an auditory continuum, Guttman (1965) suggested that

the PS may be specific to wavelength. However, using tones as

discriminative stimuli, Pierrel and Sherman (1960) obtained a PS in

rats. Bloomfield (1967) and Thomas and Lyons (1968) have also

obtained a PS on a line-tilt continuum with pigeons.

Several variables are known to be related to the occurrence of

the PS. The first is the kind of discrimination training that is

given. Orthogonal discrimination training (the discriminative stimuli

are not on the same physical continuum) results in a symmetrical

gradient with the peak at S+ (Guttman and Kalish, 1956). Non-orthogonal

discrimination training (the discriminative stimuli are both on the

same physical continuum) results in a PS (cf: Hanson, 1959). The

discrimination is established by differential reinforcement of the

stimuli.

A second important variable is the amount of responding to S-

during discrimination training. Terrace (1964) devised a procedure

that minimizes the amount of responding to S- which he called

"errorless learning". The low S- response rate was achieved by

introducing S- for very short presentations (2 sec) after preliminary

training on S+. The duration of S- presentations was then gradually

increased but Ss made few, if any, responses to S-, Learning with

gradually decreasing response rate. Terrace found that when the

discrimination was acquired without errors there was no PS in the PDG.

In a subsequent study, Terrace (1966) found that as the amount of

discrimination training increased, the PS was eliminated. After 30

sessions of discrimination training (approximately 1500 min) all 4

Ss showed the PS. After 45 discrimination sessions only two of the 4

Ss showed the phenomenon. Only one of 4 Ss showed a PS after 60

training sessions.

Characteristics of the PDG are also related to the method of

stimulus presentation during training. Honig (1962) has shown that if

the discriminative stimuli are presented simultaneously there is no

PS. Successive presentation of S+ and S- seems to be critical.

Yarczower et al. (1966), by manipulating schedules of reinforce­

ment to elicit comparable response rates to both discriminative stimul

while maintaining differential reinforcement, have shown that such

comparable rates of responding eliminate the PS. Yarczower, Gollub

& Dickson (1968) equated frequency of reinforcement in the two com­

ponents of a MULT schedule which yielded different response rates.

The PS was observed. These studies indicate that the frequency of

reinforcement is not a factor in obtaining a PS provided there is a

difference in response rates to S+ and S-.

T h e p r e s e n t study w a s c o n c e i v e d as a r e s u l t o£ f a i l u r e to o b t a i n

a PS in three different studies. The first, by Hirota, Kitson & Gray

(1969), involved two experiments, both using line-tilt and colour. In

the first experiment, Shift - No-shift, pigeons were trained to

discriminate between a red line tilted 15° left of vertical and

superimposed on a red tinted background CS+) and a similar line

tilted 15° right of vertical (S-) for the shift condition. For the

no-shift condition, the discrimination was orthogonal: a green line

tilted 15° left of vertical on a green tinted background (S+) and an

unlit key (S-). Subjects were tested for generalization to nine

line orientations (including the training stimuli) with colour

alternating evenly and the line orientations varying randomly. The

second experiment involved a Shift Left - Shift Right situation. For

the shift left condition, S+ and S- were the same as in the shift

condition of the first experiment. For the shift right condition, S+

was a green line tilted 15° right of vertical on a green tinted back-o

ground, and S~ was a similar line tilted 15 left of vertical. In

both experiments the appropriate discriminations were readily acquired

but the FDGs showed no PS. The authors suggested that the failure to

obtain the PS might have been due to the within subject design of the

generalization test.

This suggestion led to a second attempt to obtain the PS. Gray

(1970) essentially replicated the Shift - No-shift experiment of

Hirota et al. (1969) except that Ss were tested for generalization under

either the shift or the no-shift condition, but not both together.

Again, the appropriate discriminations were easily and rapidly acquired

but no PS materialized in the PDG of the shift condition.

A third study, Clarkson (1970), attempted to examine the effects

of amount of discrimination training on the development of the PS.

Using a line-tilt continuum, pigeons were trained to discriminate

between a vertical black line on a white light background (S+) and a

post-criterion discrimination training sessions, control Ss were extinguished

to 12 line orientations. For the experimental group, generalization

tests were interspersed through discrimination training. Subjects

were tested for generalization on the day following attainment of the

criterion. A second generalization test was given after six post­

criterion training sessions, and a third test after 12 post­

criterion training sessions. Again, neither group showed a PS.

In the above three studies, a VI 30 sec schedule of reinforcement

was used. In the studies cited as references by these experimenters,

a VI 1 min schedule was generally used. However, the literature does

not indicate that this difference was responsible for the absence of the

PS, Hearst, Koresko & Poppen (1964) have shown that VI 30 sec and VI

1 min schedules lead to comparable gradients of stimulus generalization.

In terms of the PS, Yarczower et al. (1966) obtained a PS using a

VI 30 sec schedule. Their PDG is quite comparable to that obtained

with a VI 1 min schedule (cf: Thomas and Burr, 1969). This suggests

that the use of the VI 30 sec schedule as opposed to the VI 1 min does

not account for the absence of the PS in the three studies under

consideration.

A review of the literature cited in these three studies revealed

that in all the PS studies, Ss had been given some single stimulus

t r a i n i n g to S + (S+ o nly t r aining) b e f o r e a c q u i r i n g the appropriate

discrimination. S+ only training in all but Bloomfield's (1967)

study entailed presentations of the stimulus that was to be used as S+

in subsequent discrimination training for a certain duration (generally

1 min) separated by time outs which generally lasted two to five

seconds, Bloomfield (1967) did not have the time out periods. In all

cases reinforcement was administered on a VI schedule. In discussing

his results, Clarkson (1970) adverted to this presence of S+ only

training and suggested that such training was a critical factor in

obtaining the PS, He concluded that the ratio of exposure to S-

to exposure to S+ must be less than unity. For example, Bloomfield

(1967) gave his Ss 14 daily one hour S+ only training sessions followed

by 14 daily one hour sessions of discrimination training on a MULT VI

1 min EXT schedule (with S+ and S- each present for 30 min per session).

The resulting S«:S+ ratio (in terms of minutes) would be 420:1260.

Clarkson gave his _Ss no S+ only training prior to discrimination

training. Since there was equal exposure to S+ and S- during

discrimination training, the ratio in this case was unity.

The literature also indicates that most PS studies have used

wavelength as the stimulus dimension. A few studies have demonstrated

the PS using other dimensions (Bloomfield, 1967, and Thomas and Lyons,

1968, used line-tilt; Pierrel and Sherman, 1960, used an auditory

dimension). The paucity of PS studies using dimensions other than

wavelength suggests the following question: is the PS reliably

obtained using another stimulus dimension? The literature does not

generally report negative results. It is, therefore, difficult to

determine how often experimenters have failed to obtain a PS. The

po i n t is a n i m p o r t a n t one. T o g e n e r a l i z e v a l i d l y f r o m the r e s u l t s

obtained using one stimulus dimension to situations involving another

dimension requires that the results be reliably obtainable in the second

situation. Thus, if Bloomfield's (1967) results, for example,

represent only one successful outcome against a background of several

that the PS is reliably obtained using a line-tilt dimension.

Because the PS was not obtained in the three studies cited

above, it seemed appropriate to attempt to replicate Hanson's (1959)

results using line-tilt as the stimulus dimension. Successful

replication would indicate two things. Further evidence of the

reliability of the phenomenon using the line-tilt dimension would be

obtained. Secondly, since the PS was not obtained in the Clarkson

(1970) study in the absence of S+ only training prior to discrimination

training, replication of Hanson's results would point to the importance

of such S+ only training in obtaining a PS, a fact not adverted to in

the literature.

Purpose of Present Research

The present study, therefore, was designed to replicate Hanson's

results using a line-tilt contimuum in order to determine whether

there is empirical evidence justifying generalizing from results of

PS studies using wavelength to the dimension of angularity. Three

experimental groups and a control condition were used. After preliminary

and S+ only training, the three experimental groups were given

o

discrimination training with 0 (vertical line) as S+ and a line tilted

30°, 45°, or 60° right of vertical as S-. These discrimination groups

are henceforth designated by the respective S- stimulus used. After

discrimination training, these groups were tested for post-discrimination

generalization to a variety of line orientations. A control group

was tested for generalization after S+ only training and again after

orthogonal discrimination training.

On the basis on Hanson's (1959) study, the following hypotheses

were tested.

I. The PDGs of experimental groups will be steeper than the

PDG of the control group in the region of S+.

11. The mode of the experimental PDGs will be displaced

away from S- in relation to the mode of the control

gradient.

III. The magnitude of this displacement will increase as the

S+, S- difference is reduced.

The independent variables were the presence or absence of non-

orthogonal discrimination training, and line orientation. The

CHAPTER II

METHOD

Subjects

Twenty commercially obtained and experimentally naive male white

Carneaux pigeons served as _Ss. Subjects were 6 - 1 2 months old at the

beginning of the experiment and were reduced by food deprivation to, and

then maintained throughout the experiment at, approximately 80% of

their free-feed body weight. There was ad lib access to water in_Ss'

home cages. Subjects were randomly assigned to four groups of five at

the beginning of training: 30°, 45°, 60°, and control groups.

Apparatus

Two standard Leheigh Valley 2-key pigeon chambers were used. The

left key in each chamger was covered. Stimuli were projected onto the

back of the right transparent response key by Grason-Stadler In-line

Digital display units. Black lines, 2.5 cm long and 3 mm wide on a

white light background, could be projected at 12 different orientations

ranging from horizontal through 180° in 15° steps. Reinforcement

consisted of a 4 sec access to a lighted food hopper containing a

g r a i n mixtu r e . D u r i n g r e i n f o r c e m e n t the s t i m u l u s k e y a n d h o u s e light

were out. The light in the food hopper was on only when reinforcement

was available. To mask extraneous sounds, white noise was provided in

the experimental chambers through speakers. A separate speaker mounted

on the wall in the room where the chambers were housed also provided

10

11

white noise. Experimental sessions were programmed from a separate

room by relays, timers, and: steppers. Responses and reinforcements

were recorded on counters and on cumulative recorders.

Procedure

Preliminary Training. This training comprised four daily

sessions. On Day 1, Ss were adapted to the experimental chambers.

(Each J received all training and testing in the same chamber.) The

house light was on but the response key was covered. Subjects

received no reinforcement. Each _S remained in the chamber for 30 min.

On Day 2, with the response key still covered, Ss were magazine

trained. This training was terminated after 60 reinforcements. On

Day 3, a vertical black line (S+) was projected on to the response key

and the key peck response was shaped using the method of successive

approximation. Shaping was terminated after 60 reinforcements. On

Day 4, 60 CRFs to S+ were given.

S+ Only Training. This training commenced on the day following

preliminary training. Each j3 received 14 daily sessions of S+ only

training on a VI 1 min schedule, each session lasting one hour,

including feeding time. S+ was continuously present except during

reinforcement.

Discrimination Training. Each S in the three experimental groups

received 14 daily sessions on a MULT VI 1 min EXT schedule with

randomly alternating 2 min periods on each component (with the

restriction that runs of either component never exceeded two). VI 1

min and EXT components were separated by a 4 sec black out. S+ was

black line tilted 30°, 45°, or 60° to the right of vertical (S-)

for the respective experimental groups. Each stimulus appeared an

equal number of times during each session (cf: Appendix A). Daily

sessions were terminated at the end of one hour (excluding feeding

time). Each S was run at approximately the same time each day. Control

Ss received orthogonal discrimination training in which S+ was the 0°

line and S» was a lighted key with no line*

Generalization Test. This test occurred on the day following the

14th session of discrimination training for experimental Ss and, for

control Ss, on the days following S+ only training and orthogonal

discrimination training. Subjects were extinguished to 12 line

orientations (including the training stimuli) which varied from 90°

left of vertical through 90° right of vertical in 15° steps. Stimuli

were presented for 30 sec periods, separated by a 4 sec black out.

Each line orientation was presented a total of eight times. The line

orientations were randomly presented with the restriction that no

stimulus could succeed itself (cf: Appendix B).

CHAPTER III

RESULTS

S+ Only Training

Figures la, lb, lc and Id show the mean response rates across

all sessions for the four groups, control, 30°, 45°, and 60°

respectively. (The performance of individual Ss in each group is

recorded in Appendix C.)

Discrimination Training

One S from the 60° group failed to acquire the discrimination

and was dropped from the experiment. Figures 2a, 2b, 2c, and 2d show

the mean response rates to S+ and S- for the control, 30°, 45°, and 60°

groups respectively. The results indicate that each group had acquired

the appropriate discrimination by Session 6 and that performance

was relatively stable throughout the remaining training sessions.

These figures also indicate that each group showed the phenomenon of

behavioral contrast (cf: Reynolds, 1961). Responses per session for

each S are recorded in Appendix D.

Generalization Test

The test for control Ss following S+ only training resulted in

flat gradient across all Ss. During S+ only training, S+ was on

continuously (except during reinforcement). Using this same procedure,

Blough (1959) and Thomas, Klipec & Lyons (1966) have obtained gradients

14

and Baron (1965) obtained gradients only when no stimulus or an orthogonal

stimulus occurred between S+ periods. They obtained flat gradients

when S+ had been on continuously. Thus, the evidence is somewhat

conflicting in this regard.

In view of the flat gradients obtained in this particular

case, control Ss were given 14 sessions of orthogonal discrimination

training and then retested for generalization.

Mean relative PDGs were computed for each group by averaging the

percentage of total responses of all Ss in a group to each test

stimulus. These results are shown in Figures 3a, 3b, 3c, and 3d for

the control, 30°, 45°, and 60° groups respectively. For all groups

the mode of the PDG was at S+. (Responses to each test stimulus are

recorded for each S in Appendix E.) Thus, when compared to the control

gradient, none of the experimental groups showed a PS.

Individual PDGs were treated as,grouped frequency distributions

(cf: Thomas and Burr, 1969) and the mean of each frequency distribution

was computed. An analysis of variance was done to determine whether

there were any significant differences among the group means. Table 1

shows the results of this analysis. The Newman-Keuls comparisons

revealed that the 30° group differed significantly (p<^.05) from all

other groups as shown in Table 2.

Using the total number of responses by a S as an estimation of

the area under the generalization gradient (cf: Hanson, 1959), an

analysis of variance was done to test the hypothesis that the areas under

the curves did not differ significantly among groups. To achieve

Table 1

Analysis of Variance of the Means of the Generalization Gradients by

Treatment Groups

Source df SS MS F

Treatment 3 510.50 170.17 5.11 '''

Error 15 499.56 33.30

Total 18 1010.06

16

Table 2

Newman-Keuls Comparisons of Means of the Generalization Gradients

C as o o 45° Co o o

c --- _{3.19 4.90} 14.08*

60° --- _{1.71 10.89*}

45° 9.18*

30°

*p <.05

17

homogeneity of variance, the raw scores were subjected to a square-

root transformation. Table 3 presents the results of the analysis of

the transformed data. Table 3 shows that areas under the curves

were comparable.

Given equal areas under the respective mean generalization gradients,

in order to test for differences in height among the gradients, the

number of responses to the modal stimulus (0°) for each S was

subjected to a square-root transformation and an analysis of variance

was done. Table 4 shows that there were no significant differences

18

Table 3

Analysis of Variance of the Means of Total Responses During Generalization by Treatment Groups

Source df SS MS F

Treatment 3 165.965 55.322 0.47

Error 15 1753.026 116.868

Total 18 1918.991

F at 3 & 15 df = 3.29 .05

19

Table 4

Analysis of Variance of Means of Total Responses to the Modal Stimulus of the Generalization

Gradient by Treatment Groups

Source df SS MS F

Treatment 3 81.911 27.304 1.57

Error 15 260.123 17.342

Total 18 342.034

R

E

S

P

O

N

S

E

S

P

E

R

M

IN

2 0

l

MEAN

180

160

140

120

100

8 0

6 0

4 0

20

0

-1

2

3

4

5

6

7

8

9

10

11

12

13

14

SESSIONS

Fig. la Mean Response Rate as a Function of S+ Only Training Sessions - Control Group.

R

E

S

P

O

N

S

E

S

P

E

R

M

IN

2 1

M E A N

180

160

140

120

100

8 0

6 0

4 0

20

1

2

3

4

5

6

7

8

9

10

11

12

13

14

SESSIONS

R

E

S

P

O

N

S

E

S

P

E

R

M

IN

2 2

MEAN

180

160

140

120

100

8 0

6 0

4 0

20

1 2

3

4

7

8

9

SESSIONS

Fig, lc Mean Response Rate as a Function of S+ Only Training Sessions - 45° Group,

R

E

S

P

O

N

S

E

S

P

E

R

M

IN

23

M E A N

180

160

140

120

100

8 0

6 0

4 0

20

1

2

3

4

5

6

7

8

9

10

11

12

13

14

SESSIONS

R

E

S

P

O

N

S

E

S

P

E

R

M

IN

24

M E A N

180

160

140

120

100

8 0

6 0

4 0

20

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

SESSIONS

Fig. 2a Mean Response Rate as a Function of Discrimination Training Sessions - Control Group: S- = no line. Horizontal Line Represents the Mean Response Rate for the Last Four Days of S+ Only Training.

R

E

S

P

O

N

S

E

S

P

E

R

M

IN

2 5

MEAN

180

160

140

120

100

8 0

6 0

4 0

20

1

2

3

4

5

7

9

SESSIONS

R

E

S

P

O

N

S

E

S

P

E

R

M

IN

2 6

180

160

140

120

100

8 0

6 0

4 0

20

1

2

3

4

5

6

7

8

9

10

11

12

13

14

SESSIONS

Fig. 2c Mean Response Rate as a Function of Discrimination Training .Sessions - S- - 45°. Horizontal Line Represents the Mean

Response Rate for the Last Four Days of S+ Only Training.

R

E

S

P

O

N

S

E

S

P

E

R

M

IN

2 7

MEAN

180

160

140

120

100

80

60

4 0

20

1

2

3

4

5

6

7

8

9

10

11

12

13

14

SESSIONS

R e p ro d u ce d w ith p e rm is sio n of the co p yr ig h t o w n e r. F u rth e r re p ro d u ct io n p ro h ib ite d w ith o u t p e rm is s io n .

MEAN

5 0

O 4 0

Q_ I/)

UJ

^

3 0

-I

20

h-z

UJ

UJ

9 0

°

75

°

6 0

°

45

°

30

°

15

°

0

°

15

°

3 0

°

45

°

6 0

°

75

°

9 0

°

LE FT

RIGHT

LINE ORIENTATION

■

Fig. 3a Generalization Gradient: Mean Per Cent Total Response as a Function of

Line Orientation - Control Group. ro

R e p ro d u ce d w ith p e rm is sio n of the co p yr ig h t o w n e r. F u rth e r re p ro d u ct io n p ro h ib ite d w ith o u t p e rm is s io n .

MEAN

5 0

UJ

O 4 0

CL

co

UJ

“

3 0

20

z

UJ

UJ

CL

O “

9 0

°

75

°

6 0

°

45

°

30

°

15

°

0

°

15

°

3 0

°

45

°

6 0

°

75

°

9 0

°

LE FT

RIGHT

LINE ORIENTATION

R e p ro d u ce d w ith p e rm is sio n of the co p yr ig h t o w n e r. F u rth e r re p ro d u ct io n p ro h ib ite d w ith o u t p e rm is s io n .

M E A N

5 0

UJ

i/)

O 4 0

Q_

10

UJ

*

3 0

20

z

UJ

UJ

9 0

°

75

°

6 0

°

4 5

°

30

°

15

°

0

°

15

°

3 0

°

45

°

6 0

°

75

°

9 0

°

L E F T

RIGHT

LINE ORIENTATION

Fig. 3c Generalization Gradient: Mean Per Cent Total Response as a Function of

R e p ro d u ce d w ith p e rm is sio n of the co p yr ig h t o w n e r. F u rth e r re p ro d u ct io n p ro h ib ite d w ith o u t p e rm is s io n .

M E A N

5 0

UJ

(/)

O 4 0

Q_ lO

UJ

“

3 0

20

h-z

UJ

cr

UJ

9 0

°

75

°

6 0

°

45

°

30

°

15

°

0

°

15

°

3 0

°

4 5

°

6 0

°

75

°

9 0

°

LE FT

RIGHT

LINE ORIENTATION

CHAPTER IV

DISCUSSION

With one exception, the results failed to support the hypotheses.

The exception occurred with respect to the first hypothesis: that the

experimental gradients would be steeper in the region of S- than the

control gradient. This prediction was supported by the results obtained

for the group with the smallest S+, S- difference, the 30° group.

The complete absence of the PS phenomenon across all experimental

Ss is somewhat puzzling. This is especially true of the 45° group

which was a replication of Bloomfield's (1967) experimental group in

which all Ss showed a PS.

Terrace (1968) has gathered evidence showing that the PS and the

phenomenon of behavioral contrast (BC) covary with manipulation of the

same variables. BC is defined as a change in the rate of responding

on one component of a multiple schedule of reinforcement in a direction

opposite to the rate of responding on the other component. In a

successive discrimination situation, this implies that the rate of

responding to S+ increases over what it would have been had there

been no extinction component (cf: horizontal lines in Figures 2a,

2b, 2c, and 2d). In the present study, all experimental Ss showed BC

even though no PS was obtained. Thus, Terrace's (1968) contention that

"a peak shift results whenever contrast occurs during discrimination

training" was not supported by the results of the present study. It

would seem, therefore, that conditions sufficient to produce BC are

32

33

not sufficient to produce a PS. This would suggest that the two

phenomenon may not be as closely related as Terrace has argued. It

may, perhaps, be more accurate to say that BC is a necessary, but not

a sufficient condition for the occurrence of a PS.

A common finding in PS studies has been the fact that when

compared to control gradients, PDGs showing the PS are noticeably

elevated (cf: Hanson, 1959; Bloomfield, 1967). The results of the

present study revealed no differences in height among the gradients.

This result is in line with the absence of the PS in the experimental

gradients.

The fact that Thomas et al. (1966) have demonstrated mirror-image

transfer in pigeons does not appear to offer a valid explanation for

the absence of the PS in the present study. These experimenters

trained two groups of pigeons to respond on a VI 30 sec schedule to

a white line tilted 30° and 60° right of vertical respectively on a

black surround. A third group was given VI 1 min EXT training on an

orthogonal discrimination task (S+ = white line tilted 30° left of

vertical on a black surround; S- = a blank key). Generalization

gradients were bimodal for all groups, each group showing a peak at

the training S+ and a peak at the mirror-image of S+. In terms of the

present study, it might be argued that inhibition built up to the

various S- line orientations transferred to the appropriate mirrdr-

images, and then generalized to surrounding stimuli, thus preventing

the occurrence of a PS. If such an assumption were valid, control Ss

should show significantly more responding to the mirror-images of the

34

inhibition to the mirror images would be virtually non-existent for

control Ss. However, the appropriate t»tests for differences of means

failed to reveal any significant differences. Moreover, such an

explanation would also have to apply to the Bloomfield (1967)

results which showed the PS. Thus, if some sort of transfer due

to mirror-image effects did occur, it was not sufficient to eliminate

the PS in Bloomfield's Ss.

One possible explanation for the absence of the PS in the present

study is that the PS cannot be reliably obtained in pigeons when the

dimension is line-tilt. The present author found two studies which

showed a PS using line-tilt (Bloomfield, 1967; and Thomas and Lyons,

1968). On the other hand, apart from the present study, the author is

aware of four experiments which failed to show the phenomenon on the

line-tilt dimension (the two experiments in Hirota et al., 1969;

Clarkson, 1970; and Gray, 1970). With the exception noted above, the

present study, using the dimension of angularity, failed to replicate

Hanson's wavelength results. Such a failure to replicate would seem to

lend some support to Guftman's (1965) caution as to the kind of

dimensions on which a PS can be obtained, and to his suggestion that

the PS may be stimulus specific. The present results may render

questionable the validity of generalizing from the results of wavelength

studies to t h e d i m e n s i o n o£ angularity.

In discussing the absence of the PS in his study, Clarkson (1970)

suggested that the pre-test ratio of S-:S+ exposure had to be less

than unity for the occurrence of a PS. The present study provided Ss

with 14 sessions of pre-discrimination training exposure to S+,

thus weighting the exposure to the discriminative stimuli in favour of

S+. However, the results of the first generalization test of control

Ss indicate that under the conditions of the present study Ss'

behavior was not under the control of the line-tilt dimension. This

suggests that Ss were not "paying attention" to S+ at this stage of

training. If it can be assumed that experimental _Ss would also have

shown flat gradients had they been tested - as noted above, the

evidence here is conflicting - then it could be argued that the S-:S+

ratio was effectively unity. This argument, however, would also apply

to Bloomfield's results since his procedure and that of the present

study for experimental Ss were identical. In this case, it would have

to be argued that the PS occurred with a pre-test S-:S+ ratio of unity.

If, on the other hand, it is argued that such S+ exposure, even though

not attended to, is sufficient to reduce the S-:S+ ratio from unity, then

results of the present study, taken together with those of Bloomfield,

would suggest that while such additional exposure to S+ may be a

necessary condition, it is not sufficient for the occurrence of the PS.

In conclusion, the present results suggest that further studies

might be done to determine whether the PS might be more a function of

the stimulus dimension used than of discrimination training itself.

Further study of the relationship between behavioral contrast and the

CHAPTER V

SUMMARY

The peak shift, identified as a displacement of the mode of the

post-discrimination gradient from S+ in a direction away from S-,

has been found to occur regularly following non-orthogonal wavelength

discrimination training, Guttman (1965) has suggested that this

phenomenon may be specific to the dimension of wavelength. In the

light of some failures to obtain a PS on the line-tilt dimension, the

possibility arose that the PS may not occur as reliably with the line-

tilt dimension as with wavelength. The purpose of the present study

was to replicate Hanson's (1959) original PS results using the

dimension of angularity.

Three experimental groups and a control group were given S+ only

training. Experimental groups were then given non-orthogonal

discrimination training in which S- was a different line orientation

for each group. Following a post-S+ only training generalization test,

control Ss were given orthogonal discrimination training. Following

discrimination training, all Ss were tested for generalization to 12

line orientations.

While behavioral contrast occurred in all Ss for all experimental

Ss the modal stimulus of the generalization gradient was S+. These

results were interpreted as giving some support to the possibility that

PS results obtained on the wavelength dimension may not be generalizable

to the dimension of angularity, and as providing some support for

36

37

G u t t m a n ’s (1965) suggestion that the PS may be a function of the

stimulus dimension used.

The results of this study further suggested that more research

might be done to examine the relationship between behavioral contrast

and the PS in order to determine whether they are as closely related

38

APPENDIX A

Order of Presentation of S+ and S-

During Discrimination Training

1. S+

2.

S-3.

S-4. S+

5.

S-6.

s+

7.

s-8.

s-9. s+

10. s+

11.

s-12.

s+

13.

s+

14.

s-15. s+

16.

s+

17.

s-18.

s-19. s+

20.

s-21. s+

22.

S-23.

s-24. s+

25.

s+

26.

s-27.

s-28. s+

29.

s-30.

s+

A P P E N D I X B

Order of Presentation of Stimuli

During Generalization Test

1. 60° Right

2. 15° Left

3. 75° Left

4. 15° Right

5. 0°

-6. 30° Left

7. 75° Right

8. 45° Left

9. 90°

-10. 30° Right

11. 60° Left

12. 45° Right

13. 60° Right

14. 90°

-15. 300 Left

16, 450 Right

17. 450 Left

18. 150 Right

19. 300 Right

20. 60o Left

21. 750 Right

22. 150 Left

23, Oo

24. 750 Left

4 0

m O O ' M l O O N O ' O H H - J t H H O O O O ' O ' - l r N v o v o o ' > 0 ' H C O ' d ' v o c o a o c o c v | . H - d ' . H r ~ ' V O c o cvi o n < f N ^ s t O ' i f l t - i < t h , o \ ' 0 ^ ' d ' h - N O o n i N C N c n ^ M n s t C v l . H < s i < N C v | n c \ l < t . H < l

-i ' ' O v O r H o o c O ' d ' a v v -i ‘ a \ c o -i n -i ' ^ o o c o a v r ^ > r H to iriOw>-i'J’O ‘nO'OO'd'a'io^-}00'd’tNiN

i r i m O ' H b ' - i M O u i c i t o O O ^ - t o o O ' t ' - i ( N H t N f O H N t n c n M H C S I c n r O H M - t r M - d '

inovcovoinoor''iNoinav<t'oorHinoQincvi

cn ooni-ivovor^or'r^ro^-icsmi^cM^-or^

H r - i a i c M c N t n o i v D ' O c n v f i N f f i c r i N f o o c r i P i ' O C S | C M r H C O r H C \ I C O C O C M r - I H N f l H N s J r - i n

t o i s c n < n o o N < f o \ c r i r - i r ^ c * i M o o M M c j \ f n < f < f O O i n O ' l N < t O ' D - C l ' f , ) N N v O s f N O O ' - I N n.CTvr^vOrHcoinrHi-^in-.d'voavoinrHcocoin C S I C V l r H C V l r H C N C O r C t N i - I H M n H n - d - H M

.h inco<No\invoiN<fovocooocoaoavcor^r'' v t ^ O H O \ C O N O \ O ^ M r - l < t v O N h " d ' f O < t c o o \ v Q r ^ o o o o o o v o v o r ' . < r r ^ a \ o o < r . - t v o c o c o CN <N h CS h N m

o X % t? •H a •rl cd H rH c o + CO 60 a •rH 3 P w <D CO c o a M <U P i in

^ o o N f f i c o i o n n t s c T ^ i o o o n n n ^ r i o i o ' O h O H O N M n ' O O ' O f f l H i o i O H P i n i o < t n O O O O O f f " O r J t N W L O N N | N r - ( ! n r - l r - I O O cn cm h c o , h cm c o M r 4 r 4 N i N H i n M M N 0 ' O N M N n - - i c o H n n h s r o N < i - \ o ^ n o M N t n v o n o M s f M t ' i ' j ' a ' o o - J N K t ' - i o C T \ C M a v ! ' ' 0 0 \ < t a \ 0 0 < t > H O C M > H C O < H v O C M O tHCMrHCMHrHCMcM cMrHCMcMcMrHCOCMrHCO

co<o<JcMoi''-vovooocMcovocovooor''CocM

<n n ^ ' j N M o o i o i o i M o o a i n n o i O N H i o i s h n o o h ( N i M D O H i r i N o o s l ' ' J h H i r i H N r-l cv) H N CS CNrHrHCMrHrHCMCMrHCM i n - f H i r i n o o ' O O c D i M N N v t a i n n ^ K t ' a ) n N H h N ^ o o N m n i o c i ' o n n i o n o o o l O ^ M N o n H i n ' o n n h n o o n i n N N ® H N i- I M H H N N rH , Hr Hr Ht H< NCMr Hr H o o ^ i o n n i o i D N i N ^ i o n o i o n ' t i o n o i v o c o v o v o o v i n a v c o i n o v r H o o H a o i n c o H i n o i - i N < i ' i N | v . ^ o o c v | v D v o H i n c O ' d ' t n i r i i n ' f n rH CM r—I rH rH rH rH i—I r—I rH iH iH rH CM rH rH rH o v c o < f v o c M | - ' . . H O I ' ' 0 ' < f ' r H C O c o o o a ' > v O C M < 0 I l ' O O O v l ' i A t ' C O i O v O H H M v f i A C O e O ' O ® i N H < t r ^ o v < t v O r H f ^ < ) - H v o v o c n H v o c n ( N i n rH CM rH t—I i—I rH Cvj rH rH t—I rH rH rH r—I r—! r—I rH

CO

H O t O h - J i n O O H H < f H

O O O O r - ' C v J l T l C O O O r H O r H C O

-jioainootsncoNstnvt

co in uv ^ vo oo oo

Q sf CO i" 00 Ht in

-5 CO cvj vo o\ co o

S'

to

Q

t N H h v O H C O H n H ' J O V H O M V l l N O O ' h l C I voniniNOhnvocciHsrvjoinooHoooaio

t O ' d " a v O O O < N v f c o o v a v ' d - < t C T v C O O < N C M c o < N r—I r—1 Cv| rH rH rH t—I rH rH 1—1 rH rH rH rH

oor^rHoo<NomvovoocoCTviNcoaoooco<fav covoavincOrHcviovQOOtncoHtcovooavoovo inovovocooocTioor>r>rHavrH(NOr^coinvo

<*>!

HvtxttV'Oioonintn'oniNonioootONO H Q O v f s t v t c o v f m wo oc n Ho no ov i - Nf vD 'f'foivoo'ininvovosfooa\oin<tina\'j® cor^vooor'COHoor^i^-vorHHoor'Oooooooo =K==fe=S==S==fe=ffe=ft==ii==S==S;=fe=t!==!fc=H==«==S==ft:=S==S= a, 3 O U o

o o o o o o o o o o o o o o o o o o i n i n m i n i n o o o o o o

v O v O v O v O ' d - v t ' ^ - c T ' d ' C O C O C O C O c O u u c_> u

R e p ro d u ce d w ith p e rm is sio n of the co p yr ig h t o w n e r. F u rth e r re p ro d u ct io n p ro h ib ite d w ith o u t p e rm is s io n . APPENDIX D

Responses During Discrimination Training

Group 60°: 60°: 60°: 60°: 45°: 45°: 45°: 45°: 45°: S # #3411 #7406 #6904 #8647 #7949 #3548 #1537 #8645 #7685

Day 1 2 3 4 5 6 7 8 9 10 11 12 13 14

42

ov Ov CM CM CO CO oo CO o co in <f CM n- rH in o o o rH rH CM Ov Ov OV in rH O <t ov CM OV ov rH o\ in OV rH rH CO m c m 00 CO rH rH in m

CM rH rH rH rH CM CM CM rH 00 <t 00 rH co c m vO vO vo r-'* in rH O <t I''- rH m o vO O CO m <r in co c m VO O ov VO VO 00 vo vo 00 rH o i— i rH CO 00 1— 1 c m c m rH CM m VO 00 VO 00 MT m rH

CO rH CM rH rH CM CM CM rH vO VO VO rH 00 rH co m O vo CO O 00 00 vo in in o rH CM vo ov r^ VO CO vO Ov 00 vO rH rH vO rH rH <1* OV CM m <t o CM vO in VO rH vo r>* CM CO rH CM rH rH CM CM CM rH

00 «n vo in rH CO rH O' ■<r o 00 o vo CM r- o o i-H rH 00 »— i 00 00 ov 00 in rH 00 CM vO rH VO CO co VO VO rH rH h- OV rH CO CO O CO CM vO 00 <t 00 CO CO rH CM rH rH CM CM CM rH CO CM CO vo m -d* rH CO VO CO o m r- CM o vD 00 o sf VO o in as oo rH in rH o co vo CO CM h- 00 H oo r^ OV rH CM CO rH in in vf* n- 00 00 CM rH CM i i rH CM cM CM rH

c m m CM O CO <f rH O CM vj- vO CM rH O O m m vO CO CO vo m r>* vo rH CM CO o vO <1* m rH

Os vO CO O i-1 CO rH co <fr VO CO m CM r- vO o

CM f— I rH CM rH rH CM CM CM CM Ov CO Ov O <t CO CM in rH vo in <1* OV CO M3 OO CO CO -i vo in h- m co in 00 N rH 00 CO i— 1 M3 oo OV 00 CM CM rH co 00 m O rH r- m

CM rH CM rH rH CM CM rH CM CM Ov o oo r-' vo in m rH vO O o c m in rH VO Ov rH ov in VO CO M3 c m in rH 00 rH VO ov CM -d- in rH T-t 00 r-> ov O <N on c m fs'» rH 00 vO in co m -i vO oo cn

c m rH rH CM rH rH CM (N ^ CM CM vO VO CM CO CO rH OV rH 00 CO in rH in rH as \o CO ov oo as rH CO 00 00 h- in oo 00 ov o co in so m rH CM in <n VO H O CO CM Ov CO m 00 .-l CM vO CO .-4

CO I— 1 rH CM rH rH CM CO CM CM Ov O rH VO ai m oo in CO oo vO o CO in as o m ov as 00 00 vo Ov 00 .-1 vf 00 in co CO OV vo oo -d- •<r co as cm in 00 ov in CO vO o co VO r-* Q VO O «— i

CM rH CM CM rH CM -5 CM CO rH 00 rH t'"'. Os I"- CO OV m oo o o c m m O 00 CO Ov CM I''-Mi* CO ov O CO r> m vo ov VO rH O CO OV rH vo •<r vO vO r- in co CO 00 Ov CM vt* vO oo CO oo as

CM rH CM CM rH CM co CM CO CM OV rH OV <f 00 cM c m as 00 VO co in co <j- vo co O CM vO 00 rH 00 in m in o as co rH CO 00 -d- ov ov in ov co CM VO O vo -d* <t VO o M0 vf r- as m CM rH t-M 03

CM rH rH rH rH CO tH CM CO -l CM <]•

oo in «n oo rH OV rH M3 O CO vO r- r^ co oo CO CO as cm

o 00 vO O 00 rH 00 O rH OV Ov vO co in vo 00 rH in t''. CM 00 CM o ov Os r- rH rH I*-. CM CO o vo oo VO rH 00 00

rH rH rH rH rH rH CO rH co CO CM rH CO cr\ r-» OV OV vo in Ov CO co ov O rH in i'' rH VO CO CO 00 rH h- in r- rH 00 rH co OV rH I CO CM o r- as cm rH rH CO 00 00 cM <t* co m Ov CM ov n*. rH O 00 <t vO o co co rH rH rH rH rH rH rH rH CM rH CM CM rH rH CM »— t fo

+ * Hh 1 4- | + 1 + I + i + 1 + 1 + 1 + 1 Q CO CO CO CO CO CO CO CO CO CO CO CO CO CO CO CO CO CO C/3 C/3

VO CO CM o co 00 CO o

ov 00 CO rH o co 00 id =& oo Ov o in in ov 00 vO rH rH 00 oo 00 00 oo

w 1 =3= =& =Ss

a,

3 .. .. .. .. .. o o o o o o o o o o

o u u u u _V o CO CO CO CO CO

43 w X M Q § PM 44 ca <v H c o •H 44 cti N •H

i— (

u <u c a> a M) 0 •0 o M a) ca G o CM co a) pi cn =s= o o vo 5 vO 00 =«= o o vO oo vO in cn CM oo VO LO cn CM a o *r4 44 Hi 44 CO CD Ml CM

O O O C M L O O C M O ' - i ' - l O O

vo cn

O O O M i - l r M l O I J I M O O O

in vo

O O v D N v D O v t h O C M O O vo cn

O O - J c M i n O H r C H C M O O *-4 vo in

O C M O O < - i O O v c n c M O O O

m

o

O O C M h H H v oN - J O O O av cn cn vo vo

-4 <f

o

o i M o c n M c f o c o i v i n v o o o vo

cm cm v o in

o o - M i n o o c M c M o o o o vo

o o o o n - o c n o o o o o

—i in

O O O ' - i ' d - O a v c n c M o O O -cl- t"

o o o ' - i c n o c o c n - i o o o

.— I r-- r—I

O O O O O V O 0 V 0 0 - - M O O O CM v o -cf

O O O O O O O - t O O O O

o o o r ' ^ M O ' - i o o o o o vo § 0'd-<tcMcnoon-or^ooo

< t c n m

|—4 1—4 ^4 1-4 1-4 pi Pi pi pi Pi G O O O O O O O O O O O O vo

o m o i n o i n o i n o i n o i n

av vo -cf cn *-t r4 cn <f vo in

ca 3 r—I 3 e •H 44 CO 00 r>-vO m cn CM oo VO m cn cm G o •H 44 cd 44 C CD ca 0) u CM

O O O O O O O O O O O O

O O O O C M r - i v j i O O O O O

o o o v o o - v O M j - o o r - ' O O

cm i n cm

o ^ o o o \ r - i c n < t ^ 4 0 o o

m m

ooav--iavcnoNOcMvoocn

r - t .-t -cT in

o c M O < r o o < t o o > - i o o o

cn cn

O O O O C O H i C h v O O N - t

-4 CM

vtO'-imin'fl'Oi-iOHocM

r4 *— I i— I vt cn Ml- cn

O 4 O 4 C 0 N M V O O M O O

r-c c n cm

O O O i - i O O v o c M v t O O O O

i—I CM c o CM

o o o o v f i n c u c M M O O o

CM CM CM CM

o o o o m r ^ c n m - 4 0 0 0

cm h cn cn

00"-icnooocMoocMr-400

CM cm CM

o o o - 4 < N c M i n c M c n o o o

h cm cn cn

o o m c o n m in M i n o o o

cm cn cn mc

O O O C M O O O 1—I O V O O O " —t O -4 vf -cf r-4

j j , j _4 _4 pi pi pi pi pi

O O O O O O O O O O O O

o i n o i n o i n o i n o i n o t n

-44 LT| <3-vO 00 =SSs O m -d m oo vo o in <r

o o o o <r *—1r—I o o o o •d o i—l vO o

00 vD oo <r asCM 00 CM

o o I" "1CM o in ON o Q\r-- o CN o o cn CMas

r - T-1VO t—1r~ i i—l CM r—i r^

i—i

n

o iH 00CM LOa m cn CM in o o cn 1—1VO n O

vO 00CTv 00r - cn i—i vO

o o 00i ! ln ON VO OvOso CTV cn o o cn CMas as

LO vo h- 00VO i—i cn in T-~i

o CN o r^ 00G\ <t 00m o oo o Nf o i—l in cn m

i—l Os O o CN Mf CM

i—l 1—1 r>

vo cn

o I-' c\cn o i—l in *<r o CN o in o o 00<r cn 00

cn r-^ 00 m 00r^» cn i—l m

=fe

o r^ LOaso 00<NasO o o o oo CM vO r-> cn

CM vo r - r^ 00 in CN cn • i CM cn i-i

o in

cn m < t o m 00 o> CMOS cn o o o o vO m

*—i CN r—1CM m r—100 <*■ cn

00

v O

in

cn

IN

O O O O t " < N O O O O O O

O O O c n c N ' C T r - i O O O t - i O cn

o —i m o o m - i - i c n o o c N

r—I *<3* i— |

O ' - i o o ' n i ' i o ' H O O f i o

O —l O O v O i N I ^ i n O O O O

O O O O C P i i —i C T i O O O O O

CN cn cn

o o o o N D o o ^ m o o o o a\

cn cn

o o o o o ^ r ^ c n o o o o

cn <n ^

J J J J J Pi Pi Pi Pi Pi

O O O O O O O O O O O O o i n o i n o i n o i n o i n o i n

a \ r ^ c o s f c n i - i i-i i n N1 i o h

CTV r-' oo in •vt cn cN a e 0 0 •H •rl ■M +J

cO CG a)

44 d j j

d H £

CD d a) W a a) <D •H a)

U •w 5^

P4 cn

cn o\ o

-d- cn

VO o CTV

N N H

r-1 o cn

< t -d- ^

O r i N O i O n H O O O t N O i—l ~d*

o o o o < N < r r ^ o v o o o - ^ < t CN

O O O O O O O O O O O O

o o o o c n o m o o o o o o o Nf

o>Hinr^cyvocin--d-oooo o cn -d- cn

O O O O O O O O O O O O

O O O O O O O O O O O O

O C N O ^ N c n O O v O O O O O

j j , j *4 j pi pi pi

o o o o o o o o o o o i n o i n o m o v n o m o\ in vo d n h h n n

w o r—1 3 0 •H 44 cn

R eproduced with permission of the copyright owner. Further reproduction prohibited w ithout permission.