The Analysis of Visual Motion: A Comparison of Neuronal and Psychophysical Performance
Updated: Sep 22, 2021
Britten et al., 1992, The Journal of Neuroscience
We compared the ability of psychophysical observers and single cortical neurons to discriminate weak motion signals in a stochastic visual display. All data were obtained from rhesus monkeys trained to perform a direction discrimination task near psychophysical threshold. The conditions for such a comparison were ideal in that both psychophysical and physiological data were obtained in the same animals, on the same sets of trials, and using the same visual display. In addition, the psychophysical task was tailored in each experiment to the physiological properties of the neuron under study; the visual display was matched to each neuron's preference for size, speed, and direction of motion. Under these conditions, the sensitivity of most MT neurons was very similar to the psychophysical sensitivity of the animal observers. In fact, the responses of single neurons typically provided a satisfactory account of both absolute psychophysical threshold and the shape of the psychometric function relating performance to the strength of the motion signal. Thus, psychophysical decisions in our task are likely to be based upon a relatively small number of neural signals. These signals could be carried by a small number of neurons if the responses of the pooled neurons are statistically independent. Alternatively, the signals may be carried by a much larger pool of neurons if their responses are partially intercorrelated.
This paper tries to answer the question: "How is the exquisite psychophysical sensitivity of human and animal observers related to the sensitivity of individual cortical neurons?".
Basically, what this paper asks is to what sense, or to what level, each neuron contributes in signaling the presence of a particular feature in the visual environment. This paper argues that psychophysical decisions in their task are likely to be based upon a relatively small number of neuronal signals, and such signals could be carried by a small number of neurons if the responses of the pooled neurons are statistically independent, or they could be carried by a much larger pool of neurons if their responses are partially inter-correlated.
(wrote some time in March, 2020)