Aims of this chapter

The patient, S.F., w ho w ill be reported in this chapter, suffered from a probable dem entia of Alzheim er's type. He show ed a severe difficulty in reading a lo u d m u ltid ig it arabic n um erals. This stu d y w as in te n d e d to in v estig ate w h e th er his deficit w as d e p e n d e n t on the p rin te d form of th e p resen ted num bers. This w as d eterm in ed by com paring S.F.'s p erfo rm an ce in read in g arabic num erals, w ritte n n u m b er nam es and w o rd s an d by e v alu atin g his perform ance in other num ber processing tasks not req u irin g the ability to read aloud num bers. S.F.’s arabic num eral dyslexia turned o u t to be selective since the p atien t show ed a well preserved ability to read aloud w ritten n u m b er nam es, letters and w ords. This clear dissociation, reported for the first tim e, realized a double dissociation w ith the "num ber sparing effect" observed in alexic patients.

The im plications of S.F's. arabic num eral dyslexia for m odels of num ber p ro cessin g w ill be ex p lo red . T h ro u g h a sy stem atic in v e stig a tio n of his perform ance in various tasks involving different com ponents of the num ber processing system and through an error analysis I will try to establish w hich of the cognitive processes involved in reading aloud arabic num erals is disrupted. The findings will be discussed in the light of the existing cognitive architectures proposed for num ber processing. O n the basis of S.F.'s perform ance on a reading aloud arabic num eral task a revision of M cCloskey et al.'s m odel of num ber

p rocessing will be p ro p o sed . In o rd er to take in to account S.F.’s read in g difficulties I will suggest a m odel for reading aloud m ultidigit arabic num erals w ith a functional arch itectu re in w hich n u m b er p ro d u c tio n processes are accessed n o t only th ro u g h in term ed iate sem antic re p re se n ta tio n s b u t also th ro u g h an "asemantic" com putation.

3.2 M ethod and results

3.21 Case report

S.F. is a 52 year-old right-handed man. H e attended school for a total of 17 years. He occupied an executive position in a bank and w as also a local leader of a political party. His past m edical history is not relevant. S.F w as first seen as an o u t-p atie n t at the Clinica N eurologica 1 in P adova in Jan u ary 1990 for an evaluation of his progressive m em ory difficulties that, according to the patient and his relatives, had started insidiously about one and a half years before. In the follow ing period, the p atien t began to develop depressive traits, m ild dressing difficulties partly d u e to difficulty in distinguishing the front from the back of clothes and some topographical disorientation episodes that posed problem s, for exam ple, in driving back home.

The p atien t rep o rted th at he had problem s w ith arithm etic. H e claim ed th at reading cheques and perform ing simple calculations w ere m ore difficult for him. The patient claimed th at such difficulties interfered w ith his work. S.F. and m em bers of his fam ily reported th at he had h ad no difficulties w ith arithm etic before his illness and given his job he daily h ad to perfo rm q u ite complex calculations. Given such problem s he was already considering the possibility of re tirin g from w ork. A fter the first o b serv atio n he w as a d m itte d to o u r d e p artm e n t for a m ore careful investigation of his condition. W hen he w as discharged, after 2 weeks, I continued to follow him as an o u t p atien t for about 4 m o n th s.

A CT scan show ed a p attern of m ild cortical atro p h y of u n k n o w n origin. The discharge diagnosis w as that of probable dem entia of the A lzheim er’s type.

The data presented w as collected between February 1990 and the beginning of June 1990. D uring this period his condition rem ained rem arkably stable. The chronological order of the tasks perform ed by the patient was:

2. Reading aloud of arabic num erals 3. Tests of calculation

4. Tests of w ritten num ber production 5 Reading aloud of w ritten n u m b er names 6. Tests of num ber recognition

7. Tests of num ber com prehension

8. Reading aloud and w riting of letters, words, nonw ords, sentences an d stories 9. N um ber repetition tasks

10. Tests of spoken num ber production

In the first two m onths, the patient was investigated one or tw o tim es a week for sessions of about one and a half hours. In the rem aining period, he was seen once a w eek for ab o u t one and a half hours. H is num erical processing abilities rem ained stable over the testing period.

A follow -up study about one and a half year later (Septem ber 1991) was perform ed, the results of w hich will be described later in chapter 4.

3.22 N eurological exam ination.

A p art from the neuropsychological signs (see below ), this w as entirely w ithin norm al limits.

3.23 N europsychological exam ination.

The patient was m ildly disoriented in tim e an d severely d isoriented in place. H e knew th at it w as w in ter b u t he w ro n g ly re p o rte d the m o n th (Novem ber instead of January) and the year (1988 instead of 1990). It w as always im possible for him to find his room in the N eurological D ep artm en t and his wife rep o rted that inside their house he had som etim es show ed difficulties in going from one room to another. His collaboration in the testing situation was good an d his m ood appropriate.

A significant discrepancy w as observed betw een his perform ance on the verbal and perform ance scales of the WAIS. He obtained a verbal IQ of 106 and a perform ance IQ of only 70. This discrepancy w as in te rp reted as indicating a degree of constructional an d visual interpretative difficulties. H is full-scale IQ w as 90. His pro-rated IQ score an d the in dividual age-scaled scores for each

su b test are given in Table 3.1. On the arithm etic su b test of the W.A.I.S. he obtained an age-scaled score of 4.

Table 3.1

W.A.I.S. Intelligence quotients and W.A.I.S. individual subtest scores

Verbal I.Q. 106

Perform ance I.Q. 70

S im ilarities 10

V ocabulary 13

Picture com pletion 6

Block design 1

Picture arrangem ent 6

Digit span 6

A rith m etic 4

The p a tien t had obvious m em ory im pairm ents in his ev ery d ay life; he show ed some difficulties in retaining new inform ation about public events and in correctly recalling recen t an d rem ote ev en ts co n cern in g his p erso n al experience. N o confabulations w ere observed. H e w as able to rep eat 6 digits forw ards and 2 digits backw ards w hen they w ere presented auditorilly, whereas, w ith visual presentation, he could repeat just 4 digits forw ards. His visuo-spatial span, as assessed by the Block tapping test (Corsi, 1972) w as 2, w ell below the n orm al range. H e was com pletely unable to leam a su p rasp an spatial sequence after 20 presentations. Similarly, he scored only 29/50 on a recognition m em ory test of faces (W arrington, 1984). Long-term verbal m em ory w as investigated with tw o learning tasks: a 10 w o rd list and paired associates (De Renzi, Faglioni and R uggerini, 1977). In both of these tasks the patient's perform ance w as grossly defective. H e was unable to learn the 10-w ord list after 20 presentations and his score on a paired associates learning test was 2,64 (threshold = 8,73; scores below the threshold are considered pathological).

H is sem antic m em ory ap p eared quite well p reserv ed ; the p a tie n t was asked to produce as m any names as he could in 60 seconds. H e w as able to give 14 fru it nam es, 15 anim al nam es and 10 car names. These scores are w ith in the norm al range (Novelli et al, 1986). H is perform ance w as flaw less (60 o u t of 60 correct answers) on a task w hich required him to p o in t to pictures belonging to different sem antic categories (fruits and vegetables, anim als, body parts, vehicles, m usical instrum ents, indoor objects) an d in a p ictu re n am in g task u sin g the sam e m aterial as the picture pointing task (60 o u t of 60 correct answ ers). His perform ance w as again flawless (64 o u t of 64 correct answ ers) in a m odified version of the "Semantic anom alies" test (Baddeley, 1976) an d in a Synonym s test (48 out of 48 correct answers).

N o v isu al, a u d ito ry o r tactile agnosia w as p re se n t. T he p a tie n t's perform ance was flawless in an Italian version of the Shallice an d Evans (1978) cognitive estim ation test (10/10). Bucco-facial and lim b praxis w ere unim paired, both on verbal com m and and on imitation. H ow ever, his d raw in g abilities were severely im p aired . H e w as u n ab le to d raw even the sim p lest item s from m em ory. H e also had severe difficulties copying geom etric figures an d he show ed the closing-in phenom enon. M arked difficulties w ere also ev id en t on a line o rien tatio n ju d g m en t task (Benton, H am sher, V arney an d Spreen, 1983) w h en none of his answ ers w ere correct. His perform ance w as also severely im paired pointing to the cardinal points and the principal cities on a blank m ap of I ta ly .

O n an initial num eracy screening test severe difficulties w ere p resen t in n u m b er processing and calculation skills. In p articu lar, S.F. a p p eared to be im p a ire d re a d in g alo u d arabic n u m erals an d o n calcu latio n task s. H is im pairm ent on num eracy tasks is described in the experim ental section later.

In sum m ary, the neuropsychological exam ination show ed the presence of a d ishom ogeneous im p airm en t of cognitive functions. The m ain difficulties ap p ea re d restricted to m em ory and visual-constructional functions. A severe im pairm ent of num eracy skills was also present.