METHODS AND MATERIALS

5.2.1 Participants

62 female participants took part in the study, all of which were either students or staff at the University of Sussex. In contrast to our previous study, participants were not recruited on the basis of fitting within high or low TFEQ-D criterion, but instead were recruited by email or responding to adverts on campus. All were naïve to the purpose of the experiment, and were instructed that the study was investigating the

relationship between personality traits and cognitive performance. All participants were fully debriefed upon completion of the study, we well as offered the opportunity to find out more via email.

5.2.1a: Participant Characteristics

Table 5.2.1.aDescriptive Statistics for Self Report Eating Measures and BMI

Mean SD Minimum Maximum

n=62 n=62 n=62 n=62

BMI 23.2 + 3.2 17 33

TFEQ-D 7.19 + 3 1 15

TFEQ-R 8.6 + 5.4 0 19

RS 12.98 + 5.25 4 26

Participants who responded to the recruitment email for the following investigation were included, provided they did not meet any of the exclusion criteria (such as previous history with eating disorders, and the full exclusion criteria is included in Appendix 5 in the consent form). BMI was not addressed as an exclusion criterion, as such, there were two obese participants in the following investigation. Moreover, TFEQ-D scores were not used to classify participants, therefore the distribution of scores for the current sample included a greater concentration of median scoring females (i.e. TFEQ-D score between 5 and 8 points).

5.2.2 Materials

5.2.2.a Three Factor Eating Questionnaire (Stunkard & Messick, 1985) Please see section 2.2.4a for a detailed description of the TFEQ scale 5.2.2.b The Revised Restraint Scale (RS) (Herman & Polivy, 1980)

The RS (Herman et al. 1978) is a ten-item questionnaire that requires participants to self assess dieting and weight fluctuation. Two factors emerge: CD Concern for Dieting, and WF Weight fluctuation, although a single score is obtained which does not differentiate between these two subscales. An original RSS is included with the scores and classification of CD versus WF items in Appendix 4.a, the remaining items that are not classified as CD or WF refer to information about participants‟ weight history. The RS is provided in Appendix 5b.

5.2.2.c Go No Go Task Parameters

In the current investigation, participants attended to five digit number sequences that were presented for 1000 ms on a Dell computer screen. Participants were instructed to click the computer mouse (left click) as soon as they were sure the subsequent 5-digit stimulus was a “Go” stimulus (and not a No Go stimulus, which changed colour to red). The initial stop signal was presented 250 ms after presentation of the Go signal, this delay dynamically adjusted depending on the participants performance, by increasing by 50 ms after an unsuccessful inhibition task, making the future trial easier, or by decreasing by 50 ms after a successful inhibition trial, making the subsequent trial more difficult. The No Go trials comprised 25% of the total trials, and Go trials comprised 25% of the trials. The remaining 50% of the trials were novel trials, during which unmatching 5-digit sequences were presented. 120 trials were presented, with 120 sec break in between trials.

5.2.3 Procedure

Each participant came to the lab for a pre-booked 20-minute test sessions. Upon arrival, the procedure of the experiment was explained and full consent obtained with

participants‟ clear awareness of their right to withdraw at any time. Please see Appendix 5a for a consent fomr. The participant was led to a testing cubicle where she received a set of instructions explaining how to complete the Go No Go task. The participant was left to complete the Go No Go task, and once the Go No Go was completed, the experimenter provided a digital version of the TFEQ task, which was also completed by the participant. After both the Go No Go and TFEQ had been finished, the experimenter directed the participant to a second cubicle where she completed the RS, and was finally weighed at the end of the experiment, with scales accurate to +/- 0.3 kg. Participants were offered a chocolate as reward for

participating, and were fully debriefed before they left.

5.3 Results

Table 5.3.a:Descriptive Statistics for Participant Characteristics and Performance on the Go No Go Task

Mean + SE (n= 62)

BMI 23.22 + 0.45

RS 12.90+ -.68

TFEQ-D 7.21 + 0.38

TFEQ-R 8.65 + 0.68

TFEQ-D+R 15.83 + 0.88

Go No Go 298 + 177

Table 5.3.a provides descriptive statistics for the current sample with regard to BMI, RS, TFEQ-D, TFEQ-R, and TFEQ-D+RA. In order to explore the inter relationships between each of the variables, Pearson‟s bi-variate correlation was conducted and results are reported in Table 5.3.b.

Table 5.3.b:Intercorrelations between Participant Self Report Measures of Eating Behaviour and Go No Go Performance

RS TFEQ-D TFEQ-R TFEQ-R+D BMI

Go No Go 0.31 ** 0.21* 0.09 0.16 0.16

RS 1.00 0.40*** 0.57*** 0.61*** 0.43***

TFEQ-D 0.40*** 1.00 0.34** 0.69*** 0.33**

TFEQ-R 0.57*** 0.34*** 1.00 0.92*** 0.27*

TFEQ-D+R 0.61*** 0.69*** 0.92*** 1.00 0.32**

BMI 0.43*** 0.33*** 0.24* 0.32** 1.00

*p<0.05, **p<0.01

In order to determine which measures of self reported Restraint had the most robust association with Go No Go performance, a stepwise multiple regression was

performed. Since previous research (Nederkoorn, 2004) had shown a significant relationship between RS and Go No Go performance, RS was entered as a forced entry variable, and the subsequent other measures (TFEQ-D, TFEQ-R, TFEQ-D+R, and BMI) were entered in as a stepwise analysis.

The regression analysis showed the model was statistically significant (F(1, 60)=

6.20, p< 0.05). The model accounts for 9.4% of the variable, which falls by 1.6%

once adjusted indicating that this model can account for 7.8% of the variance of the general population.

The current model replicated the finding that high RS scores were significantly associated with higher impulsivity on the Go No Go task (Nederkoorn, 2004).

Moreover, RS scores were the only significant predictor in the model (t=2.49, p=0.016), and Table 5.3.c provides all regression statistics.

Table 5.3.c:Final Regression Model for Self Reported Eating Behaviour and Impulsivity on the Go No Go task

B SE B Beta

Step 1

Constant 184.24 43.17

RS 8.93 3.12 0.35 **

Step 2

Constant 150.05 116.74

RS 10.09 4.05 0.39*

BMI 0.64 5.53 0.016

TFEQ-D 6.51 6.19 0.144

TFEQ-R -5.011 3.82 -0.195

TFEQ-D+R -0.72 0.46 0.72

Note: R² =0.35 for Step 1; Delta R²= 0.4 for step 2 *p<0.05, **p<0.01

Notably, there was a negative relationship between TFEQ-R and reaction time on the Go No Go, which could be interpreted as support for our previous finding, although this relationship was not significant.