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UK funding (£279,846): The brain processes underlying sensory comparison Ukri1 Jan 2019 UK Research and Innovation, United Kingdom
Overview
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The brain processes underlying sensory comparison
| Abstract | The stimuli of the natural world differ in many sensory attributes, such as lightness, hue, orientation, texture, the speed and direction of motion, and distance from the observer. So effortlessly and swiftly does the human visual system compare two stimuli with respect to one of these attributes, that there has been rather little formal discussion of how such comparisons are performed within the brain. We believe that there are two, very distinct, types of mechanism underlying such perceptual comparisons. When the comparison is local - for example, a comparison of the lightness of adjacent objects - the comparison may be performed by dedicated, hard-wired, nerve cells that draw antagonistic inputs (excitatory and inhibitory) from adjacent regions of the retina. This type of hard-wired comparison is rather well understood. Physiologists have found cells in the cortex of the brain that respond to local differences in texture, or in speed of motion or in distance from the observer. But how is the comparison performed when the observer is required to compare stimuli that fall at two well separated points within the visual field? This question has seldom been raised. Is there a hard-wired, difference-extracting nerve cell for every possible pair of positions in the visual field and for each of the properties of visual stimuli (hue, orientation, speed etc)? This seems a priori unlikely, owing to the bulk of the nerve cells and the connections that are needed. An alternative is that the brain contains a communication system that resembles the man-made Internet, in that the same fibres, from moment to moment, carry different packages of information, each associated with the addresses of the sender and of the addressee. By this account, the information about the two stimuli would be encoded in abstract form and sent over the brain's Internet (the 'cerebral bus') to a decision-making centre, perhaps in the prefrontal cortex. Our planned research has empirical and theoretical components. We propose perceptual experiments that should reveal - for particular conditions and particular visual attributes - whether the observer is using the signals from hard-wired neural comparators or is comparing more abstract representations of the two stimuli. Thus if dedicated comparator neurons are used, then the precision of comparison is expected to deteriorate with spatial separation, since lateral connections in the visual system are known to become sparser with distance. Similarly, the precision of comparison might be expected to deteriorate if the stimuli also differ in some irrelevant attribute - if, say, speed is being compared but the stimuli move in opposite directions. For dedicated comparator cells are often specific to more than one attribute of the stimulus. However, neither of these experimental manipulations may impair comparisons that depend on more abstract representations of the stimuli. The visual attributes we shall particularly concentrate on are speed and direction of motion. Two arrays of moving dots will be briefly presented at different positions in the observer's visual field and he or she will be asked to indicate which array is, say, moving faster. There is a practical interest in studying motion, since in the real world relative motion in the periphery guides our balance and our locomotion. In pilot studies, we found remarkable individual differences between people in their ability to judge the relative speed of moving arrays: our work may lead to selection tests for professions in which such judgements are critical. The theoretical part of our work is intended to prompt discussion of the format in which information is transmitted over the white-matter tracts of the brain and the 'protocol' that governs transmission. Are there specialized histological structures at the origins of the tracts? Is there 'handshaking' between transmitter and receiver, to prevent overflow of buffers? |
| Category | Research Grant |
| Reference | BB/S000623/1 |
| Status | Closed |
| Funded period start | 01/01/2019 |
| Funded period end | 30/11/2021 |
| Funded value | £279,846.00 |
| Source | https://gtr.ukri.org/projects?ref=BB%2FS000623%2F1 |
Participating Organisations
| University of Cambridge |
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