G J Brelstaff | PubMed Health

PubMed2000

A new visual illusion of relative motion.

We present a remarkably simple illusion that manifests whenever a certain class of flat static patterns are moved across our peripheral visual field. A relative motion is perceived in a direction perpendicular to the true motion. Translatory, looming, and rotational movements of the head or the pattern can all elicit it. Each pattern is constructed of simple elements that define, through luminance, an orientation polarity. This polarity could be encoded by spatiotemporally tuned, orientation sensitive units in area V1. We offer an explanation for the illusion based on how such units from V1 may be combined to feed the processes that subsequently interpret motion.

Head Movements↗

PubMed1994

Generating colour and texture verniers.

This paper describes computer graphics techniques for presenting visual stimuli in a vernier format composed out of coloured texture patterns. Such stimuli can be used to investigate the performance at the task of localising boundaries mediated by changes in colour and/or texture. We summarise the contents as follows: (1) Techniques for presenting visual stimuli are reviewed with a view to how they might be used to present colour and texture verniers. (2) The design of the vernier stimuli for the localisation task is considered. (3) Significant elements of this design are: (a) the use of non-isoplanatic textures to avoid interference effects at boundaries, (b) the modulation of the texture patterns along axes in MacLeod-Boynton colour space so that relative retinal cone contributions are controlled, and (c) the use of double-buffering, colour map manipulation, and contrast randomisation techniques to avoid problems commonly encountered when presenting computer graphics stimuli on colour monitors. (4) Results of a psychophysical experiment that presents colour and texture verniers are reported elsewhere.

Color Perception Tests↗