Introduction to the Special Issue on Multimodality of Early Sensory Processing: Early Visual Maps Flexibly Encode Multimodal Space, Multisensory Research, 3-4 (28), 249-252.

As living organisms, we have the capability to explore our environments through different senses, each making use of specialized organs and return ing unique information. This is relayed to a set of cortical areas, each of which appears to be specialized for processing information from a single sense — hence the definition of ‘unisensory’ areas. Many models assume that primary unisensory cortices passively reproduce information from each sensory organ; these then project to associative areas, which actively combine multisensory signals with each other and with cognitive stances. By the same token, the textbook view holds that sensory cortices undergo plastic changes only within a limited ‘critical period’; their function and architecture should remain stable and unchangeable thereafter. This model has led to many fundamental discoveries on the architecture of the sensory systems (e.g., oriented receptive fields, binocularity, topographic maps, to name just the best known). However, a growing body of evidence calls for a review of this conceptual scheme. Based on single-cell recordings from non-human primates, fMRI in humans, psychophysics, and sensory deprivation studies, early sensory areas are losing their status of fixed readouts of receptor activity; they are turning into functional nodes in a network of brain areas that flexibly adapts to the statistics of the input and the behavioral goals. This special issue in Multisensory Research aims to cover three such lines of evidence: suggesting that (1) the flexibility of spatial representations, (2) adult plasticity and (3) multimodality, are not properties of associative areas alone, but may depend on the primary visual cortex V1.

On the Possibility of a Unifying Framework for Serial Dependencies, i-Perception, 6(6) 1–16.

Serial effects in perception have been studied since the dawn of psychophysics. Color aftereffects greatly advanced the understanding of color vision in the 19th century, and motion aftereffects have intrigued perceptual scientists for centuries. Recent discoveries in visual attention and psychophysics have intensifed interest in such effects. The current consensus is that they are not curiosities but serve an important function and can be critical for understanding perception.
The current article summarizes the contributions to a recent conference (SFX 2014, Pisa, Italy) and underscores the idea that the brain has learned how to exploit temporal regularities in the environment.

Mechanisms for perception of numerosity or texture-density are governed by crowding-like effects,Journal of Vision, 15(5), 1-12.

We have recently provided evidence that the perception of number and texture density is mediated by two independent mechanisms: numerosity mechanisms at relatively low numbers, obeying Weber’s law, and texture-density mechanisms at higher numerosities, following a square root law. In this study we investigated whether the switch between the two mechanisms depends on the capacity to segregate individual dots, and therefore follows similar laws to those governing visual crowding. We measured numerosity discrimination for a wide range of numerosities at three eccentricities. We found that the point where the numerosity regime (Weber’s law) gave way to the density regime (square root law) depended on eccentricity. In central vision, the regime changed at 2.3 dots/82, while at 158 eccentricity, it changed at 0.5 dots/82, three times less dense. As a consequence, thresholds for low numerosities increased with eccentricity, while at higher numerosities thresholds remained constant. We further showed that like crowding, the regime change was independent of dot size, depending on distance between dot centers, not distance between dot edges or ink coverage. Performance was not affected by stimulus contrast or blur, indicating that the transition does not depend on low-level stimulus properties. Our results reinforce the notion that numerosity and texture are mediated by two distinct processes, depending on whether the individual elements are perceptually segregable. Which mechanism is engaged follows laws that determine crowding.

Strong Motion Deficits in Dyslexia Associated with DCDC2 Gene Alteration,J Neurosci, 21 (35), 8059-8064.

Dyslexia is a specific impairment in reading that affects 1 in 10 people. Previous studies have failed to isolate a single cause of the disorder, but several candidate genes have been reported. We measured motion perception in two groups of dyslexics, with and without a deletion within the DCDC2 gene, a risk gene for dyslexia. We found impairment for motion particularly strong at high spatial frequencies in the population carrying the deletion. The data suggest that deficits in motion processing occur in a specific genotype, rather than the entire dyslexia population, contributing to the large variability in impairment of motion thresholds in dyslexia reported in the literature.

The oblique effect is both allocentric and egocentric,Journal of Vision, 8 (15), 24-24.

Despite continuous movements of the head, humans maintain a stable representation of the visual world, which seems to remain always upright. The mechanisms behind this stability are largely unknown. To gain some insight on how head tilt affects visual perception, we investigate whether a well-known orientation-dependent visual phenomenon, the oblique effect—superior performance for stimuli at cardinal orientations (0° and 90°) compared with oblique orientations (45°)—is anchored in egocentric or allocentric coordinates. To this aim, we measured orientation discrimination thresholds at various orientations for different head positions both in body upright and in supine positions. We report that, in the body upright position, the oblique effect remains anchored in allocentric coordinates irrespective of head position. When lying supine, gravitational effects in the plane orthogonal to gravity are discounted. Under these conditions, the oblique effect was less marked than when upright, and anchored in egocentric coordinates. The results are well explained by a simple “compulsory fusion” model in which the head-based and the gravity-based signals are combined with different weightings (30% and 70%, respectively), even when this leads to reduced sensitivity in orientation discrimination.

Number as a primary perceptual attribute: a review, Perception 1-27 DOI: 10.1177/0301006615602599.

Although humans are the only species to possess language-driven abstract mathematical capacities, we share with many other animals a nonverbal capacity for estimating quantities or numerosity. For some time, researchers have clearly differentiated between small numbers of items—less than about four—referred to as the subitizing range, and larger numbers, where counting or estimation is required. In this review, we examine more recent evidence suggesting a further division, between sets of items greater than the subitizing range, but sparse enough to be individuated as single items; and densely packed stimuli, where they crowd each other into what is betterconsidered as a texture. These two different regimes are psychophysically discriminable in that they follow distinct psychophysical laws and show different dependencies on eccentricity and on luminance levels. But provided the elements are not too crowded (less than about two items per square degree in central vision, less in the periphery), there is little evidence that estimation of numerosity depends on mechanisms responsive to texture. The distinction is important, as the ability to discriminate numerosity, but not texture, correlates with formal maths skills.

On the Possibility of a Unifying Framework for Serial Dependencies, i-Perception, 6(6) 1–16.

erial effects in perception have been studied since the dawn of psychophysics. Color aftereffects greatly advanced the understanding of color vision in the 19th century, and motion aftereffects have intrigued perceptual scientists for centuries. Recent discoveries in visual attention and psychophysics have intensifed interest in such effects. The current consensus is that they are not curiosities but serve an important function and can be critical for understanding perception.
The current article summarizes the contributions to a recent conference (SFX 2014, Pisa, Italy) and underscores the idea that the brain has learned how to exploit temporal regularities in the environment.