The Certainty of Ambiguity in Visual Neural Representations

Perceptual Resolution of Ambiguity: Can Tuned, Divisive Normalization Account for both Interocular Similarity Grouping and Difference Enhancement

Our visual system usually provides a unique and functional representation of the external world. At times, however, the visual system has more than one compelling interpretation of the same retinal stimulus; in this case, neural populations compete for perceptual dominance to resolve ambiguity. Spatial and temporal context can guide perceptual experience. Recent evidence shows that ambiguous retinal stimuli are sometimes resolved by enhancing either similarity or differences among multiple percepts. Divisive normalization is a canonical neural computation that enables context-dependent sensory processing by attenuating a neuron's response by other neurons. Experiments here show that divisive normalization can account for perceptual representations of either similarity enhancement (so-called grouping) or difference enhancement, offering a unified framework for opposite perceptual outcomes.

Hemispheric functional asymmetries and sex effects in visual bistable perception

This study investigates bistable perception as a function of the presentation side of the ambiguous figures and of participants' sex, to evaluate left-right hemispheric (LH-RH) asymmetries related to consciousness. In two experiments using the divided visual field paradigm, two Rubin's vase-faces figures were projected simultaneously and continuously 180 s long to the left (LVF) and right (RVF; Experiment 1) or to the upper (UVF) and lower (DVF; Experiment 2) visual hemifields of 48 healthy subjects monitored with eye-tracker. Experiment 1 enables stimulus segregation from the LVF to the RH and from the RVF to the LH, whereas Experiment 2 does not. Results from Experiment 1 show that males perceived the face profiles for more time in the LVF than in the RVF, with an opposite trend for the vase, whereas females show a similar pattern of perception in the two hemifields. A related result confirmed the previously reported possibility to have simultaneously two different percepts (qualia) in the two hemifields elicited by the two identic ambiguous stimuli, which was here observed to occur more frequently in males. Similar effects were not observed in Experiment 2. These findings suggest that the percepts display the processing abilities of the hemisphere currently processing the stimulus eliciting them (e.g., RH-faces), and that females and males reflect in bistable perception, a genuine manifestation of consciousness, the well-known hemispheric asymmetry differences they show in ordinary perception.

Reappraising reappraisal: an expanded view

Reappraisal is a frequently used and often successful emotion regulation strategy. However, its underlying cognitive mechanisms are not well understood. In this paper, we seek to clarify these mechanisms by expanding upon our recently proposed reAppraisal framework. According to this framework, reappraisal consists of appraisal shifts that arise from changes to the mental construal of a situation (reconstrual) or from changes to the goals that are used to evaluate the construal (repurposing). Here we propose that reappraisal can target both object-level construals and goals representing states in the environment as well as meta-level construals and goals about different states in the mind. We also propose that reappraisal can operate by facilitating decommitment from a dominant construal or goal as well as by facilitating commitment to alternative construals or goals. We demonstrate that the 2 × 2 × 2 matrix formed by crossing the three distinctions between reconstrual and repurposing, between object-level and meta-level representations, and between decommitment and commitment operations forms a useful map of different reappraisal tactics. We draw examples of each of the 8 reappraisal tactics from basic and clinical research. We conclude by considering future research inspired by the expanded reAppraisal framework.

Multistability, perceptual value, and internal foraging

Substantial experimental, theoretical, and computational insights into sensory processing have been derived from the phenomena of perceptual multistability-when two or more percepts alternate or switch in response to a single sensory input. Here, we review a range of findings suggesting that alternations can be seen as internal choices by the brain responding to values. We discuss how elements of external, experimenter-controlled values and internal, uncertainty- and aesthetics-dependent values influence multistability. We then consider the implications for the involvement in switching of regions, such as the anterior cingulate cortex, which are more conventionally tied to value-dependent operations such as cognitive control and foraging.

Equivalent noise characterization of human lightness constancy

A goal of visual perception is to provide stable representations of task-relevant scene properties (e.g. object reflectance) despite variation in task-irrelevant scene properties (e.g. illumination and reflectance of other nearby objects). To study such stability in the context of the perceptual representation of lightness, we introduce a threshold-based psychophysical paradigm. We measure how thresholds for discriminating the achromatic reflectance of a target object (task-relevant property) in rendered naturalistic scenes are impacted by variation in the reflectance functions of background objects (task-irrelevant property), using a two-alternative forced-choice paradigm in which the reflectance of the background objects is randomized across the two intervals of each trial. We control the amount of background reflectance variation by manipulating a statistical model of naturally occurring surface reflectances. For low background object reflectance variation, discrimination thresholds were nearly constant, indicating that observers’ internal noise determines threshold in this regime. As background object reflectance variation increases, its effects start to dominate performance. A model based on signal detection theory allows us to express the effects of task-irrelevant variation in terms of the equivalent noise, that is relative to the intrinsic precision of the task-relevant perceptual representation. The results indicate that although naturally occurring background object reflectance variation does intrude on the perceptual representation of target object lightness, the effect is modest – within a factor of two of the equivalent noise level set by internal noise.

Binocularly-driven competing neural responses and the perceptual resolution of color

Competing rivalrous neural representations can be resolved at several levels of the visual system. Sustained percepts during interocular-switch rivalry (ISR), in which rivalrous left- and right-eye stimuli swap between eyes several times a second, often are attributed to competing binocularly driven neural representations of each rivalrous stimulus. An alternative view posits monocular neural competition together with a switch in eye dominance at the moment of each stimulus swap between eyes. Here, a range of experimental conditions was tested that would change the colors seen if mediated by eye dominance but not if by competition between binocularly driven responses. Observers viewed multiple chromatically rivalrous discs in various temporal and spatial patterns, and reported when all discs in view appeared the same color. Unlike typical ISR paradigms that swap the complete stimulus in each eye, some of the rivalrous discs were swapped at a different time, or faster frequency, than other discs. Monocular dominance of one eye at a time implies that all discs will rarely be seen as identical in color when some discs swap at a different frequency than others. On the other hand, competing binocularly driven neural responses are not affected by asynchronous swap timing among the individual discs. Results for every observer are in accord with competing responses at the level of binocularly driven, chromatically tuned neurons. Although an account based on eye dominance can be constructed using many small retinotopic zones that have independent timing for the moment of switching the dominant eye, competing binocularly driven responses are a more parsimonious explanation.

Lightness Perception in Complex Scenes

Lightness perception is the perception of achromatic surface colors: black, white, and shades of grey. Lightness has long been a central research topic in experimental psychology, as perceiving surface color is an important visual task but also a difficult one due to the deep ambiguity of retinal images. In this article, I review psychophysical work on lightness perception in complex scenes over the past 20 years, with an emphasis on work that supports the development of computational models. I discuss Bayesian models, equivalent illumination models, multidimensional scaling, anchoring theory, spatial filtering models, natural scene statistics, and related work in computer vision. I review open topics in lightness perception that seem ready for progress, including the relationship between lightness and brightness, and developing more sophisticated computational models of lightness in complex scenes. Expected final online publication date for the Annual Review of Vision Science, Volume 7 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.