Dynamics of contrast adaptation in central and peripheral vision

Number adaptation: A critical look

It is often assumed that adaptation - a temporary change in sensitivity to a perceptual dimension following exposure to that dimension - is a litmus test for what is and is not a "primary visual attribute". Thus, papers purporting to find evidence of number adaptation motivate a claim of great significance: That number is something that can be seen in much the way that canonical visual features, like color, contrast, size, and speed, can. Fifteen years after its reported discovery, number adaptation's existence seems to be nearly undisputed, with dozens of papers documenting support for the phenomenon. The aim of this paper is to offer a counterweight - to critically assess the evidence for and against number adaptation. After surveying the many reasons for thinking that number adaptation exists, we introduce several lesser-known reasons to be skeptical. We then advance an alternative account - the old news hypothesis - which can accommodate previously published findings while explaining various (otherwise unexplained) anomalies in the existing literature. Next, we describe the results of eight pre-registered experiments which pit our novel old news hypothesis against the received number adaptation hypothesis. Collectively, the results of these experiments undermine the number adaptation hypothesis on several fronts, whilst consistently supporting the old news hypothesis. More broadly our work raises questions about the status of adaptation itself as a means of discerning what is and is not a visual attribute.

Dynamics of sensory and decisional biases in perceptual decision making: Insights from the face distortion illusion

Bias in perceptual decision making can have both sensory and decisional origins. These distinct sources of bias are typically seen as static and stable over time. However, human behavior is dynamic and constantly adapting. Yet it remains unclear how sensory and decisional biases progress in distinct ways over time. We addressed this question by tracking the dynamics of sensory and decisional biases during a task that involves a visual illusion. Observers saw multiple pairs of peripherally presented faces that induce a strong illusion making the faces appear distorted and grotesque. The task was to judge whether one of the last two faces had true physical distortion (experimentally introduced in half of the trials). Initially, participants classified most faces as distorted as exemplified by a liberal response bias. However, over the course of the experiment, this response bias gradually disappeared even though the distortion illusion remained equally strong, as demonstrated by a separate subjective rating task without artificially distorted faces. The results suggest that the sensory bias was progressively countered by an opposite decisional bias. This transition was accompanied by an increase in reaction times and a decrease in confidence relative to a condition that does not induce the visual illusion. All results were replicated in a second experiment with inverted faces. These findings demonstrate that participants dynamically adjust their decisional bias to compensate for sensory biases, and that these two biases together determine how humans make perceptual decisions.

Effects of spatial frequency cross-adaptation on the visual number sense

When observing a simple visual scene such as an array of dots, observers can easily and automatically extract their number. How does our visual system accomplish this? We investigate the role of specific spatial frequencies to the encoding of number through cross-adaptation. In two experiments, observers were peripherally adapted to six randomly generated sinusoidal gratings varying from relatively low-spatial frequency (M = 0.44 c/deg) to relatively high-spatial frequency (M = 5.88 c/deg). Subsequently, observers judged which side of the screen had a higher number of dots. We found a strong number-adaptation effect to low-spatial frequency gratings (i.e., participants significantly underestimated the number of dots on the adapted side) but a significantly reduced adaptation effect for high-spatial frequency gratings. Various control conditions demonstrate that these effects are not due to a generic response bias for the adapted side, nor moderated by dot size or spacing effects. In a third experiment, we observed no cross-adaptation for centrally presented gratings. Our results show that observers' peripheral number perception can be adapted even with stimuli lacking any numeric or segmented object information and that low spatial frequencies adapt peripheral number perception more than high ones. Together, our results are consistent with recent number perception models that suggest a key role for spatial frequency in the extraction of number from the visual signal (e.g., Paul, Ackooij, Ten Cate, & Harvey, 2022), but additionally suggest that some spatial frequencies - especially in the low range and in the periphery - may be weighted more by the visual system when estimating number. We argue that the cross-adaptation paradigm is also a useful methodology for discovering the primitives of visual number encoding.

Repulsive Aftereffects of Visual Space

Prolonged exposure to a sensory stimulus induces perceptual adaptation aftereffects. Traditionally, aftereffects are known to change the appearance of stimulus features, like contrast, color, or shape. However, shifts in the spatial position of objects have also been observed to follow adaptation. Here, I demonstrate that visual adaptation produced by different adapter stimuli generates a bi-directional spatial repulsion. Observers had to judge the distance between a probe dot pair presented in the adapted region and compare them to a reference dot pair presented in a region not affected by adaptation. If the probe dot pair was present inside the adapted area, observers underestimated the distance. If, however, the dot pair straddled the adapted area, the distance was perceived as larger with a stronger distance expansion than compression. Bi-directional spatial repulsion was found with a similar magnitude for size and density adapters. Localization estimates with mouse pointing revealed that adaptation also affected absolute position judgments. Bi-directional spatial repulsion is most likely produced by the lines of adapter stimuli since single bars used as adapters were sufficient to induce spatial repulsion. Spatial repulsion was stronger for stimuli presented in the periphery. This finding explains why distance expansion is stronger than distance compression.

Short-Term Peripheral Contrast Reduction Affects Central Chromatic and Achromatic Contrast Sensitivity

Peripheral retinal contrast reduction is suggested as a potential myopia control strategy. However, the underlying mechanism is yet unknown. Therefore, this study investigated the influence of peripheral contrast reduction on central chromatic and achromatic contrast sensitivity (CS). A total of 19 participants were included. Peripheral contrast reduction was induced via Bangerter foils of 0.4 and 0.8 density, each with a clear central zone of 8.0 mm diameter. Central achromatic and chromatic (for S-, M-, and L-cone types) CS was measured at 3 and 12 cpd in a 2-IFC psychophysical procedure. CS was tested monocularly at 0, 30, and 90 min of adaptation time, while the fellow eye was covered by an infrared filter. With the filter in place, pupil size was controlled to be smaller than the clear central aperture. Data were analyzed using linear mixed models. Cone-type CS showed significant differences among each other (all p < 0.05), except for the achromatic and L-cone type (p = 0.87). The minimum sensitivity was found with the S-cone type and the maximum with the M-cone type. Central achromatic and chromatic CS were equally affected by diffusion. The level of peripheral diffusion also influenced CS, while the 0.8 Bangerter foil led to a higher reduction in CS compared to the 0.4 Bangerter foil (p = 0.0008) and the control condition (p = 0.05). A significant reduction in CS occurred between 30 and 90 min of adaptation time (p < 0.0001). The current study found that peripheral contrast reduction impacted central achromatic and chromatic CS equally. It further showed that the amplitude of reduction was influenced by the level of diffusion, with the reduction becoming more pronounced over time.

Changes of tuning but not dynamics of contrast adaptation with age

Normal aging results in pronounced optical and neural changes in the visual system. Processes of adaptation are thought to help compensate for many of these changes in order to maintain perceptual constancy, but it is uncertain how stable adaptation itself remains with aging. We compared the dynamics of adaptation in young (aged 19-24 years) and older (aged 66-74) adults. Contrast thresholds for Gabor patterns were tracked during and after 300 s adaptation to vertical and horizontal Gabor patches. The time course of contrast adaptation and asymptotic adaptation magnitude were similar between older and young adults when normalized for their respective baseline thresholds. Older adults showed stronger transfer of adaptation to the orthogonal orientation and there was an asymmetry between the transfer of adaptation between the horizontal and vertical orientations for both groups. These results suggest age-related changes in orientation tuning while the processes of cortical contrast adaptation remain largely intact with aging.

Interaction of contexts in context-dependent orientation estimation

The processing of a visual stimulus is known to be influenced by the statistics in recent visual history and by the stimulus' visual surround. Such contextual influences lead to perceptually salient phenomena, such as the tilt aftereffect and the tilt illusion. Despite much research on the influence of an isolated context, it is not clear how multiple, possibly competing sources of contextual influence interact. Here, using psychophysical methods, we compared the combined influence of multiple contexts to the sum of the isolated context influences. The results showed large deviations from linear additivity for adjacent or overlapping contexts, and remarkably, clear additivity when the contexts were sufficiently separated. Specifically, for adjacent or overlapping contexts, the combined effect was often lower than the sum of the isolated component effects (sub-additivity), or was more influenced by one component than another (selection). For contexts that were separated in time (600 ms), the combined effect measured the exact sum of the isolated component effects (in degrees of bias). Overall, the results imply an initial compressive transformation during visual processing, followed by selection between the processed parts.