Multisensory-inspired modeling and neural correlates for two key binocular interactions.

Most binocular vision models assume that the two eyes sum incompletely. However, some facilitatory cortical neurons fire for only one eye, but amplify their firing rates if both eyes are stimulated. These 'binocular gate' neurons closely resemble subthreshold multisensory neurons.

Muscle activity prior to experiencing the rubber hand illusion is associated with alterations in perceived hand location.

The rubber hand illusion (RHI) is a perceptual illusion in which one is made to feel that a hand-shaped object is part of their body. This illusion is believed to be the result of the integration of afferent information. However, there has been an increasing amount of evidence that suggests efferent information plays a role in this illusion as well.

A Simple Power Law Governs Many Sensory Amplifications and Multisensory Enhancements.

When one sensory response occurs in the presence of a different sensory stimulation, the sensory response is often amplified. The variety of sensory enhancement data tends to obscure the underlying rules, but it has long been clear that weak signals are usually amplified more than strong ones (the Principle of Inverse Effectiveness). Here we show that for many kinds of sensory amplification, the underlying law is simple and elegant: the amplified response is a power law of the unamplified response, with a compressive exponent that amplifies weak signals more than strong.

Hue opponency: chromatic valence functions, individual differences, cortical winner-take-all opponent modeling, and the relationship between spikes and sensitivity.

Neural spike rate data are more restricted in range than related psychophysical data. For example, several studies suggest a compressive (roughly cube root) nonlinear relationship between wavelength-opponent spike rates in primate midbrain and color appearance in humans, two rather widely separated domains. This presents an opportunity to partially bridge a chasm between these two domains and to probe the putative nonlinearity with other psychophysical data.

Developmental neurotoxicity and autism: A potential link between indoor neuroactive pollutants and the curious birth order risk factor.

Epidemiological and demographic studies find an increased risk of autism among first-borns. Toxicological studies show that some semi-volatile substances found in infant products produce adverse effects in neural and endocrine systems of animals, including behavioral and developmental effects. Several factors elevate the exposure of human infants to these chemicals.

Bridging the divide between sensory integration and binding theory: Using a binding-like neural synchronization mechanism to model sensory enhancements during multisensory interactions.

Neural information combination problems are ubiquitous in cognitive neuroscience. Two important disciplines, although conceptually similar, take radically different approaches to these problems. Sensory binding theory is largely grounded in synchronization of neurons responding to different aspects of a stimulus, resulting in a coherent percept.

Elementary visual hallucinations and their relationships to neural pattern-forming mechanisms.

An extraordinary variety of experimental (e.g., flicker, magnetic fields) and clinical (epilepsy, migraine) conditions give rise to a surprisingly common set of elementary hallucinations, including spots, geometric patterns, and jagged lines, some of which also have color, depth, motion, and texture.

To honor Fechner and obey Stevens: relationships between psychophysical and neural nonlinearities.

G. T. Fechner (1860/1966) famously described two kinds of psychophysics: Outer psychophysics captures the black box relationship between sensory inputs and perceptual magnitudes, whereas inner psychophysics contains the neural transformations that Fechner's outer psychophysics elided.

Neural interactions between flicker-induced self-organized visual hallucinations and physical stimuli.

Spontaneous pattern formation in cortical activity may have consequences for perception, but little is known about interactions between sensory-driven and self-organized cortical activity. To address this deficit, we explored the relationship between ordinary stimulus-controlled pattern perception and the autonomous hallucinatory geometrical pattern formation that occurs for unstructured visual stimulation (e.g.

Fechner-Benham subjective colors do not induce McCollough after-effects.

Fechner-Benham subjective color is widely believed to be governed by local interactions in early (probably retinal) mechanisms. Here we report three lines of phenomenological evidence that suggest otherwise: subjective colors seen in spatially extended stimuli (a) are dependent on global aspects of the stimuli; (b) can become multistable in position; and (c) even after being stabilized do not support the creation of McCollough's colored after-effects--a cortically based phenomenon generally thought to be more central than Fechner-Benham color. These phenomena suggest a central locus that controls perception of subjective color, characterized by pattern dependent interactions among cortical mechanisms that draw their inputs from peripheral units.

Inertia and memory in ambiguous visual perception.

Perceptual multistability during ambiguous visual perception is an important clue to neural dynamics. We examined perceptual switching during ambiguous depth perception using a Necker cube stimulus, and also during binocular rivalry. Analysis of perceptual switching time series using variance-sample size analysis, spectral analysis and time series shuffling shows that switching times behave as a 1/f noise and possess very long range correlations.

Sensory recoding via neural synchronization: integrating hue and luminance into chromatic brightness and saturation.

If neural spike trains carry information in the frequency and timing of the spikes, then neural interactions--such as oscillatory synchronization--that alter spike frequency and timing can alter the encoded information. Using coupled oscillator theory, we show that synchronization-based processing can be used to integrate sensory information, resulting in new second-order sensory percepts signaled by the compromise frequency of the coupled system. If the signals to be coupled are nonlinearly compressed, the coupled system behaves as if it signals the product or ratio of the uncoupled signals, e.

A role for cortical crosstalk in the binding problem: stimulus-driven correlations that link color, form, and motion.

The putative independence of cortical mechanisms for color, form, and motion raises the binding problem-how is neural activity coordinated to create unified and correctly segmented percepts? Binding could be guided by stimulus-driven correlations between mechanisms, but the nature of these correlations is largely unexplored and no one has (intentionally) studied effects on binding if this joint information is compromised. Here, we develop a theoretical framework which: (1) describes crosstalk-generated correlations between cortical mechanisms for color, achromatic form, and motion, which arise from retinogeniculate encoding; (2) shows how these correlations can facilitate synchronization, segmentation, and binding; (3) provides a basis for understanding perceptual oddities and binding failures that occur for equiluminant and stabilized images. These ideas can be tested by measuring both perceptual events and neural activity while achromatic border contrast or stabilized image velocity is manipulated.

What do catastrophic visual binding failures look like?

Ordinary vision is considered a binding success: all the pieces and aspects of an image are bound together, despite being processed by many different neurons in several different cortical areas. How this is accomplished is a key problem in visual neuroscience. The study of visual binding might be facilitated if we had ways to induce binding failures.

Spatiotemporal characteristics of hemodynamic changes in the human lateral prefrontal cortex during working memory tasks.

The prefrontal cortex (PFC) is widely believed to subserve mental manipulation and monitoring processes ascribed to the central executive (CE) of working memory (WM). We attempted to examine and localize the CE by functional imaging of the frontal cortex during tasks designed to require the CE. Using near-infrared spectroscopy, we studied the spatiotemporal dynamics of oxygenated hemoglobin (oxy-Hb), an indicator of changes in regional cerebral blood flow, in both sides of lateral PFC during WM intensive tasks.

Sensorimotor adaptation to violations of temporal contiguity.

Most events are processed by a number of neural pathways. These pathways often differ considerably in processing speed. Thus, coherent perception requires some form of synchronization mechanism.

Perception of spatiotemporal random fractals: an extension of colorimetric methods to the study of dynamic texture.

Recent work establishes that static and dynamic natural images have fractal-like l/falpha spatiotemporal spectra. Artifical textures, with randomized phase spectra, and 1/falpha amplitude spectra are also used in studies of texture and noise perception. Influenced by colorimetric principles and motivated by the ubiquity of 1/falpha spatial and temporal image spectra, we treat the spatial and temporal frequency exponents as the dimensions characterizing a dynamic texture space, and we characterize two key attributes of this space, the spatiotemporal appearance map and the spatiotemporal discrimination function (a map of MacAdam-like just-noticeable-difference contours).

Perception of forbidden colors in retinally stabilized equiluminant images: an indication of softwired cortical color opponency?

In color theory and perceptual practice, two color naming combinations are forbidden-reddish greens and bluish yellows-however, when multicolored images are stabilized on the retina, their borders fade and filling-in mechanisms can create forbidden colors. The sole report of such events found that only some observers saw forbidden colors, while others saw illusory multicolored patterns. We found that when colors were equiluminant, subjects saw reddish greens, bluish yellows, or a multistable spatial color exchange (an entirely novel perceptual phenomena); when the colors were nonequiluminant, subjects saw spurious pattern formation.

The Leaning Tower of Pisa effect: an illusion mediated by colour, brightness, and motion.

We report a novel, easily observed, and extraordinarily striking optical illusion mediated by interactions of colour, brightness, form, and motion perception--the Leaning Tower of Pisa (LTOP) illusion. Under some circumstances, the perception of orientation of coloured forms is radically altered by rotary movement. We demonstrate that this kinetic effect--easily reproduced with a common record turntable--is optimised by particular colour and brightness differences between foreground and background with an illusory tilt of 8 degrees and more.

Very short-term visual memory via reverberation: a role for the cortico-thalamic excitatory circuit in temporal filling-in during blinks and saccades?

There is a large projection of neurons from Layer VI of V1 that makes excitatory connections on LGN relay cells. It has been proposed that this circuit is involved in signal processing and thalamic sensitivity regulation. Alternatively, Crick has suggested that the circuit could be a reverberatory loop-a site for very short-term (iconic) visual memory.

Evidence of spatial and temporal channels in the correlational structure of human spatiotemporal contrast sensitivity.

1. The statistical correlation of detection thresholds for pairs of stimuli should be higher for stimuli detected by the same mechanism than for stimuli detected by different mechanisms--a property that can be used to probe the visual mechanisms that underlie detection. 2.

Cortical simple cells can extract achromatic information from the multiplexed chromatic and achromatic signals in the parvocellular pathway.

P cells, which carry both achromatic and chromatic information, are largely responsible for achromatic acuity and contrast sensitivity. The P cell achromatic information must be separated from the chromatic information to be useful. Cortical simple cells are well suited to the extraction of achromatic information by spatial bandpass filtering.