Cálculo de la fuerza de impacto en un accidente

The local level m ean accuracy for Stimulus 8 (an E m ade out of O's) is m uch greater than its global level m ean accuracy or those for both global and local level m ean accuracies for Stim ulus 6 (a circle m ade out of F's). Subject AA 's comm ents seem to reflect the relative difficulty of draw ing the local elements of the stimuli.

That all WS subjects asked to describe the stimuli were able to take account of b o th the global configuration and local elem ents indicates that there any dissociation betw een global and local levels does not lie in perception.

EXECUTION OF DRAW INGS

Anecdotal observation of the execution of draw ings by subjects w ith WS gives further sup p o rt to the hypothesis that the problem in rep ro d u ctio n of the global level elem ents lies in p lanning of the response. One subject, NN, drew for stim ulus 8 (the E m ade out of Os): a vertical line of Os, followed by a horizontal lines of Os at the top of the vertical line - see Figure A below; this was followed by a second horizontal line of Os below the first b u t not in the m iddle of the vertical line as w ould be necessary for a perfect E - see figure B below. The subject then paused, and added 3 further horizontal lines spaced evenly w ith the gap betw een the first 2, so as to fill the entire space created by the vertical line. The result - see figure C below - can hardly be called a perfect E, b u t the im pression is not of a subject w ho is unable to perceive any of the global configuration.

FIGURE A FIGURE B FIGURE C

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Q q O O O O O q O O O O O 0 0 ° 0 0 0 0 0 0 0 0 0 0 o O O O O O 0 0 0 0 0 0 0 0

Some of the other WS subjects did not com plete the closed configuration of the global elements such as the D of stim ulus 2. The im pression given w as that they had grow n bored of the task and felt they had done enough. One other subject, EE, indeed asked w hether he really "needed to do all the Ls up to there" to complete the D.

This evidence is im pressionistic, b u t indicates again th at the problem for WS subjects in rep ro d u cin g the global elem ents of hierarchical stim uli lies in planning and execution of the draw ing, rather than a dissociation in visuo-spatial perception.

D I S C U S S I O N

The experim ental hypotheses for the control groups w ere supported. There is a significant effect of age on both the global and local levels m ean accuracies, the older subjects being more accurate in their draw ings, and on the difference betw een the global and local levels, the difference being greater for the 5-year-old subjects than for the 3-year-old subjects. In addition, the results very closely tally w ith those obtained by other age groups of children by Stiles (in press), although different stimuli were used in the two studies.

A lthough there is a difference betw een the local level and global level m ean accuracies in the WS group, w ith the local level m ore accurate than the global level, this difference is not significant. Only 5 subjects w ithin the group show ed a positive local level bias. For the other 8, there was no significant difference betw een accuracies for the two levels. It is not possible to claim, as Bellugi et al. do, that aU WS subjects are incapable of reproducing the global configuration of an hierarchical stimulus.

Younger norm al controls also have a local level bias (local level mean accuracy greater than global level mean accuracy), but this is not a significant difference. The m ost appropriate m easure for the m ental age of WS subjects on this task is the test age for the Ravens Spatial matrices task. The chronological age of norm al controls corresponds to their test age on the Ravens task. If the global and local level m ean accuracies of the WS subjects are corrected according to predictions m ade from their Ravens test ages on the developm ental trajectories of the level accuracies of norm al subjects, they do not match. The local level bias show n by the 5 WS subjects' subgroup cannot therefore be explained by a sim ilar m echanism of that show n in young norm al controls.

The problem , how ever, does not seem to lie in visuo-spatial perception, as Bellugi et al. (1988) claim. 12 WS subjects, including all of the 5 show ing a positive local level bias, w ere able to describe accurately verbally all the stimuli. Only 1 out of those 5, II, consistently indicated the local level elements first, w hereby one can hypothesise a

w eak bias tow ards the local elements that m ay be perceptual in basis. O ne o th er subject, QQ, spontaneously said w hilst trying to d raw stim ulus D2, "I can't do a D m ade out of Ls". If subjects can describe the hierarchical stimuli accurately in words, then they cannot be said to be incapable of perceiving the global level. Rather, the problem m ust lie in planning and execution of the m otor response. This is borne out by qualitative analysis on stages in the process of drawing.

This stu d y does not bear out the view that WS subjects are incapable of perceiving the global configuration, the w hole object, above the local elem ents, the parts of that object. Rather, for those subjects w ho do show a dissociation on this task, it appears to be a result of a problem in planning and execution of the m otor response of draw ing. As such, it is unlikely that the ability or inability of subjects on this task will be able to explain the lack of a dem onstrable whole object assum ption default constraint. This will be discussed in the conclusion, section B.4.

B .3 .5 IS T H E T A X O N O M I C A S S U M P T I O N P R E S E N T I N