Color–motion asynchrony assessed along the chromatic axes and with luminance variation

Front. Integr. Neurosci.

2015

Area V5 of the visual brain, first identified anatomically in 1969 as a separate visual area, is critical for the perception of visual motion. As one of the most intensively studied parts of the visual brain, it has yielded many insights into how the visual brain operates. Among these are: the diversity of signals that determine the functional capacities of a visual area; the relationship between single cell activity in a specialized visual area and perception of, and preference for, attributes of a visual stimulus; the multiple asynchronous inputs into, and outputs from, an area as well as the multiple operations that it undertakes asynchronously; the relationship between activity at given, specialized, areas of the visual brain and conscious awareness; and the mechanisms used to “bind” signals from one area with those from another, with a different specialization, to give us our unitary perception of the visual world. Hence V5 is, in a sense, a microcosm of the visual world and its study gives important insights into how the whole visual brain is organized—anatomically, functionally and perceptually.

Section: The Riddoch Syndromementioning

confidence: 99%

Area V5â€”a microcosm of the visual brain

Front. Integr. Neurosci.

2015

“…What these pairing experiments show is that these different attributes of a visual scene are not perceived simultaneously. Instead, colour is perceived before orientation (form) and orientation before motion [9,[12][13][14][15][16], the perceptual asynchrony between colour and motion being as large-in neural terms-as 80 ms. The functional specialization of the visual brain thus appears to be projected in time.…”

Section: The Problem: Asynchronous Perceptionmentioning

confidence: 99%

A massively asynchronous, parallel brain

2015

Phil. Trans. R. Soc. B

Whether the visual brain uses a parallel or a serial, hierarchical, strategy to process visual signals, the end result appears to be that different attributes of the visual scene are perceived asynchronously—with colour leading form (orientation) by 40 ms and direction of motion by about 80 ms. Whatever the neural root of this asynchrony, it creates a problem that has not been properly addressed, namely how visual attributes that are perceived asynchronously over brief time windows after stimulus onset are bound together in the longer term to give us a unified experience of the visual world, in which all attributes are apparently seen in perfect registration. In this review, I suggest that there is no central neural clock in the (visual) brain that synchronizes the activity of different processing systems. More likely, activity in each of the parallel processing-perceptual systems of the visual brain is reset independently, making of the brain a massively asynchronous organ, just like the new generation of more efficient computers promise to be. Given the asynchronous operations of the brain, it is likely that the results of activities in the different processing-perceptual systems are not bound by physiological interactions between cells in the specialized visual areas, but post-perceptually, outside the visual brain.

“…Psychophysical pairing experiments show that, though they are processed in parallel, colour and directional motion are not necessarily processed with the same speed or reach a perceptual endpoint at the same time, indicating that different attributes are processed at different speeds, that is asynchronously. Over brief time windows, we see (and become aware of) different visual attributes at different times, with colour leading directional motion by about 80 ms and form (orientation) by about 40 ms (Moutoussis & Zeki, ; Arnold et al ., ; Viviani & Aymoz, ; Clifford et al ., ; Linares & López‐Moliner, ; Self, ; Žaric et al ., ). This perceptual asynchrony is also shown by the different activity time courses in different visual areas, in response to viewing the same dynamic, complex natural scenes in action movies (Bartels & Zeki, ).…”

Section: Introductionmentioning

confidence: 99%

Multiple asynchronous stimulus‐ and task‐dependent hierarchies (STDH) within the visual brain's parallel processing systems

2016

Eur J of Neuroscience

Results from a variety of sources lead ineluctably to a re-appraisal of the hierarchical and parallel processing strategies used by the brain to construct an image of the visual world. Contrary to common supposition, there are at least three "feed-forward" anatomical hierarchies that reach the primary visual cortex (V1) and the visual areas outside it, in parallel. These anatomical hierarchies do not conform to the temporal order with which visual signals reach and activate V1 and the specialized visual areas.Furthermore, neither the anatomical hierarchies nor the temporal order predict the perceptual hierarchies. The latter shows that we see (and become aware of) different visual attributes at different times, with colour leading form (orientation) and visual motion, even though it is signals from fast moving stimuli that are the earliest to reach the visual cortex (of area V5). Parallel processing, on the other hand, is much more ubiquitous than commonly supposed, but is subject to a barely noticed but fundamental aspect of brain operations, namely that different parallel systems operate asynchronously with respect to each other and reach perceptual end-points at different times.This re-assessment leads to the conclusion that the visual brain is constituted of multiple, asynchronously operating, task-and stimulus-dependent parallel hierarchies even within systems sub-serving a single attribute such as form or visual motion; which of these parallel anatomical hierarchies has temporal and perceptual precedence at any given moment is stimulus-and task-related and critically dependent upon the visual brain's ability to undertake multiple operations asynchronously.