Modelo de Análisis del Sistema

of results. For example, if a subject had responded in the 4 affirmative to the identification of two specific pictures

within a set and had been told that he was correct, this knowledge would ensure that his responses would be negative

to the remaining pictures’in the set, whether or not he was -J certain on the basis of visual information alone.

On completion of the experiment subjects were interviewed by the experimenter and invited to comment on

any aspect of the experiment. I

4.14 Results and Preliminary Discussion (i) Picture Memory.

The recognition performance of subjects is shown in table III.

No subject in either group made any errors at all in the correct identification of the stimulus category. In the control condition performance across subjects was extremely consistent, although, as predicted, some errors were made with respect to the identification of specific pictures within each homogeneous set. (mean errors - 6.5; S.D. ~ 1.8).

However, subjects scored a mean of

87%

within each homogeneous set of pictures. This performance

i

memory for faces condition of the experiment of Goldstein and Chance, described earlier (p. 80 ), and probably reflects the lesser homogeneity across the entire set of pictures in the present experiment.

Performance across subjects in the experimental

101 TABLE III Group Subject _% MM 0 5 KB 0 7 LO 0 7 DL 0 6 Control DR 0 . 4 DM 0 10 GP 0 8 BS 0 5 Mean/8.D. 0/0 6.5/1.8 PT 0 15 IG 0 18 JP 0 16 Exptl. BC 0 10 GB 0 15

m

stimulus category

E2 number of errors in relation to identi- fication of specifici pictures.

“f

102

mean number of errors in relation to the identification of specific pictures was over twice as great as for the control group. There was no significant difference at the 0.05 level between the unbiased estimates of the population

variances of the experimental and control groups (P = 0.478; Vi =* 7, V2* 5). Thus, for this parameter, the variances of the two populations were homogeneous, and a normal ’t’ test could be used to test the significance of the difference between the sample means.

The difference between the mean number of specific picture errors (E2 in table 1X3) made by the experimental and control groups was found to be significant at the 0.002% level (t = 6.9, 12 degrees of freedom).

These results very strongly support the experimental hypotheses derived from the theory, i.e. that subjects in the dual-task condition would make more specific picture errors than those in the control condition who could dedicate all their cognitive processing capacities to performance of the .recognition task. The E2 error distributions of the two

groups does not even overlap, just touching at one point. It seems apparent that the effect observed in this experiment is a very powerful one, and that the imposition of the

simultaneous internalised cognitive task upon the picture recognition task has the empirical effect on performance specifically predicted by the present theory.

An extremely important result of the experiment is that, on the basis of picture memory performance with respect to the correct identification of the 10 heterogeneous

stimulus categories alone (E^), there was no difference what­ soever between the experimental and control groups, each group

103

performing perfectly. It is only when the second index of performance (E2) is utilised that the very great differences between the groups in picture memory performance become clearly apparent. Thus, in a dual-task situation such as that used in the present experiment, it is highly probable that no differences between experimental and control groups would be found if only heterogeneous stimuli were used* On

the basis of this argument it would appear that subjects in *1 the usual type of picture memory experiment need not devote

their maximum cognitive processing capacity to the task in order to perform at the very high performance levels typically observed.

The lack of any errors by subjects of either group in identification of the heterogeneous categories is proof that subjects were always processing at least a sufficient proportion of the visual information array to correctly identify this aspect.

It is important to note that, even though subjects in the experimental group made a large number of errors in comparison to the control group, they still scored 69.68% correct responses.

(ii) Analysis of error patterns in picture memory performance

As stated earlier (p. 77), Standing (1973) has pointed out that there exists no straightforward objective method which may be employed to dimension the nature of a complex picture such as a normal photograph. Consequently, it is impossible, with the natural photographs used in the present experiment, to control precisely for equality of memory difficulty, either across the heterogeneous categories

or within the homogeneous sets forming these categories. Therefore, it is to be expected that different categories will present varying degrees of difficulty to subjects.

Table IV shows, for experimental and control groups, the total percentage of errors made by all subjects with respect to the homogeneous pictures in each set, for each of the 10 stimulus categories.

TABLE IV