Interactions between simultaneous contrast and adaptation to gradual change of luminance

Following adaptation to a field of light which was modulated by a rising ramp so that it repetitively grows gradually brighter, a steady test field of light appears to be gradually growing dimmer. In this study, if a small grey spot of constant luminance was centered in the brightening field, it appeared to be growing gradually dimmer by simultaneous contrast. This apparent dimming led to a brightening aftereffect in the spot. It was shown that this spot aftereffect had two independent components: the apparent dimming of the adapting spot produced its own aftereffect (contrast produced an aftereffect) and also the dimming aftereffect in the surround field spatially induced an aftereffect into the spot during the test period (aftereffect produced simultaneous contrast). Thus simultaneous contrast can both precede and follow successive contrast in the visual system.

A length aftereffect from grating adaptation: now you see it ... now you don't

Adaptation to a grating of short bars has the effect of increasing the apparent length of a subsequently viewed test bar, and adaptation to a grating of long bars has the effect of decreasing the apparent length of a subsequently viewed test bar. However, decreasing the interspace between the long adaptation bars has the effect of (1) negating the length aftereffect and (2) reducing the apparent width of the test bar viewed by the retina previously adapted to the grating of long bars.

Interocular transfer of movement after-effects in schizophrenia

A group of 16 chronic schizophrenic subjects were compared with 15 age-matched control subjects for interocular transfer of movement after-effects. Contrary to the hypothesis that schizophrenic subjects would show a deficit on this measure schizophrenics showed increased transfer compared to the controls. This effect is not due to response perseveration and is not correlated with length of hospitalization, age or dose of antipsychotic drugs. It is suggested that the effect reflects a deficit in 'inhibitory processes' in schizophrenia.

Stimulus persistence and age

Stimulus persistence theory states that the effects of stimulation are longer lasting in the nervous system of the old person than the younger one. This concept and its relation to perceptual functioning and age was examined via two perceptual aftereffect tasks, the Spiral and the Waterfall. Twenty-four elderly adults (mean age = 65.5) and twenty-four young adults (mean age = 24.8) were each exposed to both stimulus displays, at four exposure durations: 45, 60, 90, and 120 seconds. Following the offset of each display, the duration of any apparent motion aftereffect was recorded. Although on the basis of stimulus persistence theory it was expected that the elderly would exhibit longer mean aftereffects than the young, no support for this hypothesis was noted. Possible explanations of these results and their relation to previous findings, in terms of fatigue effects and sample characteristics, are discussed.

The site of binocular rivalry suppression

Two experiments were performed to localize the site of binocular rivalry suppression in relation to the locus of grating adaptation. In one experiment it was found that phenomenal suppression of a high-contrast adaptation grating presented to one eye had no influence on the strength of the threshold-elevation aftereffect measured interocularly. Evidently information about the adaptation grating arrives at the site of the aftereffect (presumably binocular neurons) even during suppression. In a second experiment 60 s of grating adaptation was found to produce a short-term reduction in the predominance of the adapted eye during binocular rivalry. These findings provide converging lines of evidence that suppression occurs at a site in the human visual system after the locus of grating adaptation and, hence, after the striate cortex.

Perceptual reactance and task performance

57 female subjects participated in a study in which perceptual reactance was assessed by the kinesthetic figural aftereffects test. Subjects identified as augmenters were quicker than reducers on a disjunctive reaction time task and a significant interactive effect was found on a paired-associate task. Augmenters performed better on a similar list while reducers were more effective on a dissimilar list.

The relational determination of length illusions and length aftereffects

When two lines were presented simultaneously, in an illusion paradigm, the judged length of one of the lines (the focal line) assimilated toward the length of the contextual line. When the lines were presented sequentially, in an aftereffect paradigm, the apparent length of the focal line was displaced away from the length of a previously presented contextual line (i.e. contrast). The largest effects obtained at inverse contextual-to-focal length ratios: 1.67:1 for contextual lines longer than the focal line and 0.60:1 for contextual lines shorter than the focal line. Overestimation of focal length was larger than underestimation for both illusions and aftereffects despite the fact that identical stimuli produced effects in opposite directions in the two paradigms. Results were discussed in terms of a neural length-coding model and were related to visual size constancy.

Internally augmented displays: Contingent aftereffects as performance aids

Previous research on visual contingent aftereffects has been concerned with examining the effects of various parameters (e.g., spatial frequency and luminance) on the adaptation to, and decay of, contingent aftereffects. The current study tested the viability of using visual contingent aftereffects in a display context. Using established characteristics of contingent aftereffects, a program of contingent aftereffect adaptation was designed. Studies were conducted to determine if subjects who were adapted to see visual contingent aftereffects invoked by a visual display could achieve more rapid or certain identification of a display under low luminance conditions. The results confirmed (a) that contingent aftereffects can improve performance on a visual discrimination task requiring information from a display and (b) that contingent aftereffects are more enhanced at low levels of illumination.

Sex differences in familial correlations for visual and kinesthetic aftereffects

72 subjects from 16 families performed a visual and kinesthetic aftereffect task where data were also obtained on the pretest variability and on the adjustment times. Considerable sex differences were found, such that for mothers pretest variability correlated positively with magnitude of kinesthetic and negatively with magnitude of visual aftereffect. Daughters showed more pretest variability on both tasks and much larger individual differences on the visual task than sons. These sex differences complicate any attempt at genetic analysis. However, there was some indication of X-linked inheritance in males for magnitude aftereffect and of autosomal inheritance of visual adjustment time in females.

McCollough effect and eye optics

Astigmatism induced by cylindrical lenses leads to colour sensations similar to the McCollough effect. Consequences for the design of experiments and a new interpretation of the McCollough effect are suggested.