Taking advantage of the way in which Charles Taylor hinges his account of the rise of modern secularity around the year 1500, this article attempts a reassessment of some aspects of early modern thought which have been prominent in recent studies. In particular, it focuses on the thin boundary between illusion and reality, on the lure of scepticism, and on the changing role of the Aristotelian notion of phronêsis in human action.

This paper examines the contribution of cross-cultural studies to our understanding of the perception and representation of space. A cross-cultural survey of the basic difficulties in understanding pictures—ranging from the failure to recognise a picture as a representation to the inability to recognise the object represented in the picture— indicates that similar difficulties occur in pictorial and nonpictorial cultrues. The experimental work on pictorial space derives from two distinct traditions: the study of picture perception in “remote” populations and the study of the perceptual illusions. A comprison of the findings on pictorial space perception with those on real space perceptual illusions. A comparison of findings on pictorial space perception with those on real space perception and perceptual constancy suggersts that cross-cultural differences in the perception of both real and representational space involve two different types of skills: those related exclusively to either real space or representational space, and those related to both. Different cultural groups use different skills to perform the same perceptual tasks.

Shapiro et al. (2004) introduced a new visual effect (the induced contrast asynchrony) that demonstrates a perceptual separation between the response to a modulated light and the response to contrast of the light relative to background. The effect is composed of two physically identical disks, one surrounded by a dark annulus and the other by a light annulus. The luminance levels of both central disks were modulated in time, producing a stimulus with in-phase luminance modulation and antiphase contrast modulation. Observers primarily perceived the disks to be modulating asynchronously (i.e. they perceived the contrast), but at low temporal frequencies could also track the luminance level. Here we document that the induced contrast asynchrony disappears when the surrounds are achromatic and the center lights are modulated near the equiluminant axis. Observers viewed 1-deg-diameter disks embedded 2-deg-diameter achromatic surrounds. The chromaticity of the disks was modulated in time (1 Hz) along lines in an S versus Luminance cardinal color plane and an L-M versus Luminance cardinal color plane; observers responded as to whether the modulation appeared in phase. For all observers and both color planes, the lights appeared in phase most frequently at angles near the standard observer's equiluminant line and out of phase at angles further away from that line. Observers differed in the range of angles that produce the appearance of in-phase modulation. The results suggest that induced contrast asynchronies may be useful as a technique for equating luminance of disparate lights.

The Zoellner illusion is a geometric distortion occurring when nonorthogonal inducing lines appear to tilt veridically parallel bars. The retinal pathways contributing to such illusions are unknown. The goal of this experiment was to investigate the retinal origin of the illusion. This was accomplished by determining the contrast gain for illusion thresholds. The magnocellular (MC-) and parvocellular (PC-) pathways exhibit different contrast gains, and this difference can be used psychophysically to identify the pathway. The stimulus pattern was four vertical bars with a series of inducing lines. The bars were always 5% higher in contrast than the inducing bars. The pattern was presented on a larger pedestal. Two paradigms were used. In the pulsed-pedestal paradigm, the observer adapted to the background and the pedestal and pattern were presented together as a brief pulse. In the steady-pedestal paradigm, the observer adapted to the continuously presented pedestal and the pattern appeared as a brief pulse. The contrast between the pedestal and the pattern was varied to obtain thresholds for two criteria: perceiving the directions of the inner inducing lines, and perceiving the distortion of the bars. The results for both criteria were similar in shape, but displaced in sensitivity. Detection of the directions of the inner inducing lines was 0.16–0.29 log unit more sensitive than perception of the illusion. The data for the pulsed-pedestal paradigm depended on the contrast between the pedestal and the pattern and produced a shallow V-shape. These results were associated with mediation in the PC-pathway. The data for the steady-pedestal paradigm depended on the pedestal luminance in a linear relation and showed similar sensitivity to the data for the pulsed-pedestal paradigm. Perception of the illusion required 10–15% Weber contrast.

Evidence for a dichotomy between the planning of an action and its on-line control in humans is reviewed. This evidence suggests that planning and control each serve a specialized purpose utilizing distinct visual representations. Evidence from behavioral studies suggests that planning is influenced by a large array of visual and cognitive information, whereas control is influenced solely by the spatial characteristics of the target, including such things as its size, shape, orientation, and so forth. Evidence from brain imaging and neuropsychology suggests that planning and control are subserved by separate visual centers in the posterior parietal lobes, each constituting part of a larger network for planning and control. Planning appears to rely on phylogenetically newer regions in the inferior parietal lobe, along with the frontal lobes and basal ganglia, whereas control appears to rely on older regions in the superior parietal lobe, along with the cerebellum.

A recent finding that individuals with autism are not susceptible to illusions has been explained by Happé (1996) as a sign of “weak central coherence” at lower levels of processing. We investigated the phenomenon with a more sophisticated measure. In Experiment 1, individuals with autism, Asperger's syndrome, moderate learning difficulties, and typical development adjusted certain comparison lines and circles to make them appear to be the same size in four visual illusions. With a minor exception, the participants with autism and Asperger's syndrome evinced a systematic bias in their judgements in the illusion condition. The extent of this was no different from control participants. In a second experiment, a similar finding was obtained in a task where participants made verbal judgements about the stimuli. The results suggest that lower-level coherence in visual processing in autism is intact.