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TOWARD ANIMAL MODELS OF ATTENTION AND CONSCIOUSNESS
Abstract
Carlos Brody
The Unified Percept Hypothesis and its Quantitative Neurophysiological Implications.
The properties of objects in the world that our brain perceives seem to be represented by the activity of large populations of neurons. These neurons have noisy varying firing rates. Nevertheless, single properties seem, subjectively, to have single values: for example, although the tone of a pure sinewave sound will be represented by many noisy neurons, what we consciously "hear" is a single pure sound. I suggest that, at some level of processing, the mutli-neuron representation is "unified" in the sense that although the neurons are noisy and variable, they are all correlated and vary together. Such a unified multi-neuron representation would thus encode a single, scalar, value, which would correspond to our single percept. The magnitude of the noisy variations in our percept can be determined psychophysically, by measuring the Just Noticable Difference (JND) between two stimuli. If we know the tuning curves of neurons participating in the unified representation, the JND in turn predicts, in quantitative terms, the magnitude of the covariations between the neurons. For any particular cortical area where tuning curves to stimuli are known or measurable, this quantitative prediction allows determining the number of experimental trials that would, in practical terms, be needed to measure the "unification" phenomenon if it were present. Therefore, this link between the magnitude of the JND and the magnitude of the neuronal covariations can be used as an experimental guide or "yardstick", enabling us to evaluate the experimental paradigms best suited, or not suited, for exploring the hypothesis described here.
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