LA CONSTITUCIÓN CENTRALISTA DE 1836

4.1.3.1 Data Analysis fo r Ye s / No Response and fo r Reaction Times

In the hybrid design old-new recognition task, subjects were presented with a sequence o f trials, some o f which were signals (stimuli already shown, or ‘old’) and others noise (new stimuli that had not been presented to the subjects previously or ‘new’). Signal detection theory was used as an index o f recognition memory. The number o f times each subject made a hit, i.e., said ‘yes’ to recognising an ‘old’ stimulus, and the number o f times each subject gave a false positive response, i.e., said ‘yes’ to recognising a ‘new’ stimulus were recorded for each individual subject. D-prime values were then obtained for each subject. A one sample t-test was performed on the overall d-prime scores to see if they differed from zero. This was found to be the case: d! = 0.95, t(jg) = 6.38, p < 0.001. Therefore, subjects performed significantly above chance at distinguishing between ‘old’ and ‘new’ stimuli.

Subjects’ reaction times were recorded for making a YES / NO decision to each individual stimulus item. The mean reaction times for the 7 cases, by type, are given in Table 13.

T a b le 13. E x p erim en t 12: R eaction tim es in M S for correct and in co rrect re sp o n ses collap sed o v er all stim u lu s types.

Category Type M e a n SD

OLD CATS a n d OLD DOGS 976.27 258.43

NEW CATS a n d n e w d o g s 1248.02 462.75

OLD HEAD / NEW BODY 1299.71 562.98

NEW HEAD / OLD BODY 1285.23 480.81

HYBRIDS: OLD HEAD/NEW BODY 1265.35 429.22

HYBRIDS: NEW HEAD/OLD BODY 1283.60 723.04

A repeated measures ANOVA was performed to test for differences amongst the means of the reaction times. Although there was an overall effect o f reaction time, F(,]4,6) = 2.71, P < 0.02, on a post hoc analysis (Tukey’s HSD) the

only differences in reaction times were between the OLD CATS and OLD DOGS and

the other stimuli types (as shown in Figure 30). A subsequent analysis, however, showed that there was a significant difference in subjects’ responses, depending on whether they gave correct or incorrect responses. An ANOVA revealed that subjects were significantly faster at making a correct response than an incorrect response: F(5j)= 22.64, P < 0.006 (see Figure 31).

The results o f the reaction times suggest that although subjects were using what may have been the most diagnostic properties o f the stimuli (the head and face) when categorising the animals, body information was also being processed. If only the head were used for observing the stimuli, there should be no difference in reaction times between the OLD CATS and DOGS seen in both phase 1 and phase 2

and those stimuli for which subjects had only seen the head before. Nor should there have been any differences in reaction times between correct and incorrect responses. This will be discussed further in the general discussion.

Memory Decision Task - 2000 ms Presentation Time H O O i 1200 1282.SJ 1249.74 1248.4) lOOO 4 0 (

Old Cats A Dogs New Cats* Dogs New Htad/Old Body Old Head New Body

Figure 30. Experim ent 12: Subjects were significantly faster in their reaction times for recognising the w h o l ec a t s and d o g s they had seen in phase 1 than any o f the other stim ulus

types.

Memory Decision Task - 2000 ms Presentation Time: Reaction Time for Correct & Incorrect Responses

MS

1477J8

1078.17^ ^

Correct Incorrect

J

Figure 31. Experim ent 12: M ean reaction times for correct and incorrect responses collapsed over all stim ulus types.

4.2 Experiment 13

Experiment 12 provided evidence that when processing time is relatively short, subjects focussed on the highly-diagnostic dimensions / properties o f the stimuli (the head / face area). The reaction time data, however, indicated that the less diagnostic body information was not ignored. The implication o f such findings is that although the response data suggest that dimensional processing was being used, in fact, configurai processes were also being employed. If the assumption is that those properties that are processed the fastest are those that are most critical for identification and subsequent classification purposes, then this suggests that dimensional or featural processes are employed when processing time is limited. One reason why subjects may have used configurai processing, however, is that a 2000 ms presentation is not particularly rapid. It would seem that in everyday life the identification o f objects is often made within milliseconds. Therefore, presenting subjects with the stimuli for 2000 ms may have been enough time for subjects to go on and identify the less-diagnostic properties, such as the body. This hypothesis is tested in Experiment 13.

4.2. J Method

4.2.1.1 Subjects

Subjects were 15 undergraduate students from University College London, 7 males and 8 females. Subjects were paid £2.00 for their participation. None o f the subjects had taken part in any other experiments connected with this thesis.

4.2.1.2 Design and Stimuli

The stimuli and procedure was exactly the same as Experiment 13, with the exception that subjects were presented with the stimuli for 500 ms duration in the Trial Phase as opposed to 2000 ms.