Peter Thompson

Since Milner and Goodale's `perception' and `action' streams supplanted `parvo' and `magno' as the thinking man's visual system dichotomy of choice, the race has been on to reveal these streams in the normal visual system. The early front runner has been the proposal that visual illusions affect the `perceptual', world-based ventral system but not the `action', ego-based, dorsal system. We have probed this claim in a series of experiments utilising pointing accuracy towards the endpoints and midpoint (marked or unmarked) of the Judd illusion. Further we have investigated the effects of interposing a delay between stimulus presentation and the required response. Dorsal stream representations are short lived, and visually guided actions must switch to world based (perceptual) frames of reference after a short delay, allegedly. Thus pointing performance should become equivalent to perceptual performance after a delay. We find that, perceptually, subjects...

Wohlgemuth, having measured the duration of the motion aftereffect (MAE), instructed subjects to close their eyes immediately after adaptation for a period of time longer than the MAE. Upon opening their eyes the subjects reported a residual effect, albeit somewhat shorter than the original effect. Thus the decay of the aftereffect appeared to have been retarded by the period of darkness. This effect is known as ‘storage’ and poses a problem for any model of the MAE based on the fatiguing of direction-selective units in the visual pathway. A reexamination is made of storage of the MAE, again concentrating on the intervening stimulation between movement adaptation and aftereffect test. The results suggest that the nature of the intervening pattern between adaptation and test conditions is remarkably unimportant. A total of 11 different storage patterns were examined after adaptation to high-contrast drifting horizontal sinewave gratings. For 10 of these patterns large and robust stor...

Faces are found generally to be perceived as thinner when viewed upside down. When a face is viewed upright, the internal features are thought to influence the perception of face shape. However, when inverted, it has been proposed that disruption to holistic processing means that these factors can no longer be used to judge the shape of a face. We show that it is not the case that an inverted face reverts to some average shape whereby fat faces appear thinner upside down whereas thin faces appear fatter. The fact that the illusion appears to occur for most face shapes is discussed with regard to the horizontal-vertical illusion.

Our ability to perceive many aspects of the human face is so acute that some would propose that we possess specialised face-processing mechanisms. One example of this exquisite performance is our ability to discriminate differences in the lateral separation of the eyes in pairs of otherwise identical faces—see Kemp et al (1990, Perception19 531–543). However, we have found that our ability to estimate our own interpupillary distance (IPD) shows no such accuracy. Subjects were asked to indicate, without undue rumination, their own IPD and, by way of control, the distance from the bridge to the tip of their own nose. Compared to the true distances, IPD was overestimated by more than 30% while nose length was underestimated by 11%. Although a plausible reason for the nose length underestimation is foreshortening of the image, the reason for the overestimation of eye separation remains obscure.

Vision Res. Vol. 22, pp. 377 lo 380. 1982 Printed in Great Britain 0042-6989/82/030377-04103.00 /0 Pergamon Press Ltd PERCEIVED RATE OF MOVEMENT DEPENDS ON CONTRAST PETER THOMPSON* The Psychological Laboratory, University of Cambridge, Cambridge, ...

Abstract. Mayhew and Frisby (1978) demonstrated that patterns which differ markedly in their spatial-frequency content may be very hard to discriminate. This they took as evidence against any model which proposes that the processes underlying texture discrimination ...