Perceptual learning in Vision Research

https://www.cell.com/trends/cognitive-sciences/pdf/S1364-6613(15)00252-1.pdf

No-Report Paradigms: Extracting the True Neural Correlates of Consciousness

Normal perception involves experiencing objects within perceptual scenes as real, as existing in the world. This property of “perceptual presence” has motivated “sensorimotor theories” which understand perception to involve the mastery of sensorimotor contingencies. However, the mechanistic basis of sensorimotor contingencies and their mastery has remained unclear. Sensorimotor theory also struggles to explain instances of perception, such as synesthesia, that appear to lack perceptual presence and for which relevant sensorimotor contingencies are difficult to identify. On alternative “predictive processing” theories, perceptual content emerges from probabilistic inference on the external causes of sensory signals, however, this view has addressed neither the problem of perceptual presence nor synesthesia. Here, I describe a theory of predictive perception of sensorimotor contingencies which (1) accounts for perceptual presence in normal perception, as well as its absence in synesthesia, and (2) operationalizes the notion of sensorimotor contingencies and their mastery. The core idea is that generative models underlying perception incorporate explicitly counterfactual elements related to how sensory inputs would change on the basis of a broad repertoire of possible actions, even if those actions are not performed. These “counterfactually-rich” generative models encode sensorimotor contingencies related to repertoires of sensorimotor dependencies, with counterfactual richness determining the degree of perceptual presence associated with a stimulus. While the generative models underlying normal perception are typically counterfactually rich (reflecting a large repertoire of possible sensorimotor dependencies), those underlying synesthetic concurrents are hypothesized to be counterfactually poor. In addition to accounting for the phenomenology of synesthesia, the theory naturally accommodates phenomenological differences between a range of experiential states including dreaming, hallucination, and the like. It may also lead to a new view of the (in)determinacy of normal perception.

/pdf/a-predictive-processing-theory-of-sensorimotor-contingencies-sqfgvr9ad3.pdf

A predictive processing theory of sensorimotor contingencies: explaining the puzzle of perceptual presence and its absence in synesthesia

The Craik-O’Brien-Cornsweet (COC) effect demonstrates that perceived lightness depends not only on the retinal input at corresponding visual areas but also on distal retinal inputs. In the COC effect, the central edge of an opposing pair of luminance gradients (COC edge) makes adjoining regions with identical luminance appear to be different. To investigate the underlying mechanisms of the effect, we examined whether the subjective awareness of the COC edge is necessary for the generation of the effect. We manipulated the visibility of the COC edge using visual backward masking and continuous flash suppression while monitoring subjective reports regarding online percepts and aftereffects of adaptation. Psychophysical results showed that the online percept of the COC effect nearly vanishes in conditions where the COC edge is rendered invisible. On the other hand, the results of adaptation experiments showed that the COC edge is still processed at the early stage even under the perceptual suppression. These results suggest that processing of the COC edge at the early stage is not sufficient for generating the COC effect, and that subjective awareness of the COC edge is necessary.

/pdf/awareness-of-central-luminance-edge-is-crucial-for-the-craik-51wu5hwg6h.pdf

Awareness of Central Luminance Edge is Crucial for the Craik-O'Brien-Cornsweet Effect.

Object perception is one of the most remarkable capacities of the primate brain. Owing to the large and indeterminate dimensionality of object space, the neural basis of object perception has been difficult to study and remains controversial. Recent work has provided a more precise picture of how 2D and 3D object structure is encoded in intermediate and higher-level visual cortices. Yet, other studies suggest that higher-level visual cortex represents categorical identity rather than structure. Furthermore, object responses are surprisingly adaptive to changes in environmental statistics, implying that learning through evolution, development, and also shorter-term experience during adulthood may optimize the object code. Future progress in reconciling these findings will depend on more effective sampling of the object domain and direct comparison of these competing hypotheses.

Neural Representations for Object Perception: Structure, Category, and Adaptive Coding

The perception of even the most elementary features of the visual environment depends strongly on their spatial context. In the study reported here, we asked at what level of abstraction such effects require conscious processing of the context. We compared two visual illusions that alter subjective judgments of brightness: the simultaneous brightness contrast illusion, in which two circles of identical physical brightness appear different because of different surround luminance, and the Kanizsa triangle illusion, which occurs when the visual system extrapolates a surface without actual physical stimulation. We used a novel interocular masking technique that allowed us to selectively render only the context invisible. Simultaneous brightness contrast persisted even when the surround was masked from awareness. In contrast, participants did not experience illusory contours when the inducing context was masked. Our findings show that invisible context is resolvable by low-level processes involved in surface-brightness perception, but not by high-level processes that assign surface borders through perceptual completion.

/pdf/contextual-illusions-reveal-the-limit-of-unconscious-visual-1b8p8ycs49.pdf

Contextual Illusions Reveal the Limit of Unconscious Visual Processing

Experience Shapes the Utility of Natural Statistics for Perceptual Contour Integration

Auditory modulation of visual stimulus encoding in human retinotopic cortex.

How the brain constructs a coherent representation of the environment from noisy visual input remains poorly understood. Here, we explored whether awareness of the stimulus plays a role in the integration of local features into a representation of global shape. Participants were primed with a shape defined either by position or orientation cues, and performed a shape-discrimination task on a subsequently presented probe shape. Crucially, the probe could either be defined by the same or different cues as the prime, which allowed us to distinguish the effect of priming by local features and global shape. We found a robust priming benefit for visible primes, with response times being faster when the probe and prime were the same shape, regardless of the defining cue. However, rendering the prime invisible uncovered a dissociation: position-defined primes produced behavioural benefit only for probes of the same cue type. Surprisingly, orientation-defined primes afforded an enhancement only for probes of the opposite cue. In further experiments, we showed that the effect of priming was confined to retinotopic coordinates and that there was no priming effect by invisible orientation cues in an orientation-discrimination task. This explains the absence of priming by the same cue in our shape-discrimination task. In summary, our findings show that while in the absence of awareness orientation signals can recruit retinotopic circuits (e.g. intrinsic lateral connections), conscious processing is necessary to interpret local features as global shape.

https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.2010.1909

Interpreting local visual features as a global shape requires awareness.

The ability to detect and identify targets in cluttered scenes is a critical skill for survival and interactions To solve this challenge the brain has optimized mechanisms for capitalizing on frequently occurring regularities in the environment Although evolution and development have been suggested to shape the brain's architecture in a manner that resembles these natural statistics, we provide novel evidence that short-term experience in adulthood may modify the brain's functional organization to support integration of signals atypical of shape contours in natural scenes Although collinearity is a prevalent principle for perceptual integration in natural scenes, we show that observers learn to exploit other image regularities (ie, orthogonal alignments of segments at an angle to the contour path) that typically signify discontinuities Combining behavioral and functional MRI measurements, we demonstrate that this flexible learning is mediated by changes in the neural representations of behaviorally relevant image regularities primarily in dorsal visual areas These changes in neural sensitivity are in line with changes in perceptual sensitivity for the detection of orthogonal contours and are evident only in observers that show significant performance improvement In contrast, changes in the activation extent in frontoparietal regions are evident independent of performance changes, may support the detection of salient regions, and modulate perceptual integration in occipitotemporal areas in a top-down manner Thus experience at shorter timescales in adulthood supports the adaptive functional optimization of visual circuits for flexible interpretation of natural scenes

/pdf/flexible-learning-of-natural-statistics-in-the-human-brain-icjmcq8xkn.pdf

D. Samuel Schwarzkopf

Papers

Contextual Illusions Reveal the Limit of Unconscious Visual Processing

Experience Shapes the Utility of Natural Statistics for Perceptual Contour Integration

Auditory modulation of visual stimulus encoding in human retinotopic cortex.

Interpreting local visual features as a global shape requires awareness.

Flexible Learning of Natural Statistics in the Human Brain