On mathematical illusions

A criticism of Walker’s (1973) paper on the grounds that its physiological premises lack support, that it misrepresents the theoretical position of Blakemore, Carpenter, and Georgeson (1970), and that its theory is contradicted by existing evidence.     

On the non-additivity of visual tilt illusions

In Experiment I, the visual tilt illusion induced by two orthogonal lines was found to differ from the sum of the illusions induced by each line independently. The length of one of the orthogonal-inducing lines was varied in Experiment II with the other inducing line remaining a fixed length. As length increased from zero (no line) to 100%, the size of the illusion increased monotonically. The increase in illusion was not due to the increasing length of the variable line alone since, in the absence of the line of fixed length, increasing the length of the variable line produced no significant trend in the illusion (Experiment III).     

On the susceptibility of adaptive memory to false memory illusions

Previous research has shown that survival-related processing of word lists enhances retention for that material. However, the claim that survival-related memories are more accurate has only been examined when true recall and recognition of neutral material has been measured. In the current experiments, we examined the adaptive memory superiority effect for different types of processing and material, measuring accuracy more directly by comparing true and false recollection rates. Survival-related information and processing was examined using word lists containing backward associates of neutral, negative, and survival-related critical lures and type of processing (pleasantness, moving, survival) was varied using an incidental memory paradigm. Across four experiments, results showed that survival-related words were more susceptible than negative and neutral words to the false memory illusion and that processing information in terms of its relevance to survival independently increased this susceptibility to the false memory illusion. Overall, although survival-related processing and survival-related information resulted in poorer, not more accurate, memory, such inaccuracies may have adaptive significance. These findings are discussed in the context of false memory research and recent theories concerning the importance of survival processing and the nature of adaptive memory.     

The surface and deep structure of the waterfall illusion

The surface structure of the waterfall illusion or motion aftereffect (MAE) is its phenomenal visibility. Its deep structure will be examined in the context of a model of space and motion perception. The MAE can be observed following protracted observation of a pattern that is translating, rotating, or expanding/contracting, a static pattern appears to move in the opposite direction. The phenomenon has long been known, and it continues to present novel properties. One of the novel features of MAEs is that they can provide an ideal visual assay for distinguishing local from global processes. Motion during adaptation can be induced in a static central grating by moving surround gratings; the MAE is observed in the static central grating but not in static surrounds. The adaptation phase is local and the test phase is global. That is, localised adaptation can be expressed in different ways depending on the structure of the test display. These aspects of MAEs can be exploited to determine a variety of local/global interactions. Six experiments on MAEs are reported. The results indicated that relational motion is required to induce an MAE; the region adapted extends beyond that stimulated; storage can be complete when the MAE is not seen during the storage period; interocular transfer (IOT) is around 30% of monocular MAEs with phase alternation; large field spiral patterns yield MAEs with characteristic monocular and binocular interactions.     

Idealism and illusions

According to the idealist, facts about phenomenal experience determine facts about the physical world. Any such view must account for illusions: cases where there is a discrepancy between the physical world and our experiences of it. In this article, I critique some recent idealist treatments of illusions before presenting my own preferred account. I then argue that, initial impressions notwithstanding, it is actually the realist who has difficulties properly accounting for illusions.     

Illusory illusions: the significance of fixation on the perception of geometrical illusions

Some well-known geometrical illusions disappear when the eyes are fixating and saccades are suppressed for a period of time. This disappearance is not accompanied by fading due to stabilisation of the retinal image. Any saccade made on purpose restores the illusion immediately. The fixation time after which some illusions disappeared was measured for four illusions and four subjects each. Effects of practice have been observed after measurements were repeated on successive days. Present theories of vision cannot readily explain the effect.     

Figural after-effects and apparent size

Sutherland (1954) obtained results which suggest that when the retinal size of test and inspection figures is equal, the direction of the FAE may be determined by the relative apparent sizes of the two figures. Other investigators have reproduced this result when exactly the same conditions were used: when the conditions were changed the result was not obtained. In the present paper these results are discussed and an attempt is made to determine why the effect is not obtained with small variations in the experimental conditions. It is further shown that some FAE phenomena cannot be explained by the two main existing theories; these phenomena could be explained if some analysis of the stimulus is being performed before the stage of the nervous system at which the process underlying FAEs occurs. Some recent physiological evidence (Hubel and Wiesel, 1959) supports this hypothesis. If this hypothesis is correct, it is likely that further work on FAEs determined by apparent size may help to throw light on the physiological mechanisms underlying size constancy, and some further experiments are suggested.     

Three- and two-dimensional motion after-effects

Abstract.— The principle of perceptual vector analysis proposed by Johansson (1W) implicitly assumes the organism to be equipped with physiological systems sensitive to common and divergent components of change in the proximal stimulation. The present investigation was designed to study these units by means of the after-effect paradigm. It was found that prolonged viewing of complex changes produced after-effects of motion in depth and changing form specific to the common and divergent components of change in the stimulation. Data supported an explanation of these after-effects in terms of adaptation of units selectively sensitive to different kinds of motion vectors.     

The after-effects of ventriloquism

Subjects were tested for both ear-hand and eye-hand co-ordination before and after monitoring a synchronous series of noise bursts and of light flashes coming from the same spatial position, but with the virtual position of the flashes displaced 15° laterally by prisms. Attention was forced on both stimuli by the instruction to detect occasional reductions in intensity. No subject reported noticing the spatial discrepancy. Nevertheless ear--hand co-ordination was shifted in the direction of the prismatic displacement, and eye-hand co-ordination in the opposite direction. Both shifts were observed with instructions suggesting that the sound and the light came from one single source, with instructions suggesting two separate sources, and also with no information regarding the spatial relationship of sound and light. It is concluded that the resolution of auditory-visual spatial conflict involves recalibrations of both visual and auditory data and that these alterations last long enough to be detected as after-effects.     

Interdigital transfer of kinesthetic after-effects

Two experiments investigated the effect of using a different finger for inspection (I) than is used in making judgments on the size of a kinesthetic aftereffect (KAE). Experiment I investigated transfer of I stimulation of the ring finger to judgments made with the index finger, A control group used the index finger for both judgments and 1 period. Results indicated significant KAE for both groups. Experiment II replicated Experiment I except the second finger was used to test for transfer of I stimulation to judgments made with the index finger. Results indicated KAE for only the control group which used the index finger for both judgments and 1 stimulation.     

Imagery and memory illusions

This article provides a summary of current knowledge about memory illusions. The memory illusions described here focus on the recall of imagined events that have never actually occurred. The purpose is to review theoretical ideas and empirical evidence about the reality-monitoring processes involved in memory illusions. Reality monitoring means deciding whether the memory has been perceptually derived or been self-generated (thought or imagined). A few key findings from the literature have been reported in this paper and these focus on internal source-monitoring judgments which distinguish perceptual events from imagined events. Finally, the experimental paradigms used to shed light on processes occurring in the failure of reality monitoring in healthy subjects may be extended to an examination of the causes and the prevention of hallucinations in patients.     

Perceiving the present and a systematization of illusions

Over the history of the study of visual perception there has been great success at discovering countless visual illusions. There has been less success in organizing the overwhelming variety of illusions into empirical generalizations (much less explaining them all via a unifying theory). Here, this article shows that it is possible to systematically organize more than 50 kinds of illusion into a 7 × 4 matrix of 28 classes. In particular, this article demonstrates that (1) smaller sizes, (2) slower speeds, (3) greater luminance contrast, (4) farther distance, (5) lower eccentricity, (6) greater proximity to the vanishing point, and (7) greater proximity to the focus of expansion all tend to have similar perceptual effects, namely, to (A) increase perceived size, (B) increase perceived speed, (C) decrease perceived luminance contrast, and (D) decrease perceived distance. The detection of these empirical regularities was motivated by a hypothesis, called "perceiving the present," that the visual system possesses mechanisms for compensating neural delay during forward motion. This article shows how this hypothesis predicts the empirical regularity.