Abstract
We have previously shown that the responses of V1 to dynamically presented Glass patterns are well predicted by a quasi-linear model of spatial summation within the receptive field (Smith et al., 2002, J Neurosci). We have now extended these observations to neurons in V2, recorded in opiate-anesthetized macaque monkeys.
As in V1, V2 neurons respond most selectively to translational Glass patterns when dot-pair orientation matches the best orientation measured with gratings, and when dot spacing is roughly half the period of the best spatial frequency. Also as in V1, neuronal selectivity decreases in a predictable way when the dot spacing is made smaller or larger than optimum. Perhaps because their receptive fields are larger, V2 neurons respond somewhat better to Glass patterns than V1 neurons, but rarely as well as they respond to gratings.
To explore the possible role of the receptive field surround in shaping responses to extended forms defined by Glass patterns, we measured the responses of some V2 cells to Glass patterns defining complex forms like radial and circular patterns. We arranged these forms so that the classical receptive field stimulus was always similar to the optimal translational pattern. Responses to all stimuli of this kind were very similar to the response elicited by a simple translational pattern.
We conclude that a) V2 receptive fields, like their V1 cousins, respond to Glass patterns that “match” the classical receptive field, and b) embedding the optimal local pattern in different global forms made no discernible difference to neuronal response. V2 neurons do not appear to be the neural substrate of the mechanisms, inferred from psychophysical experiments, that give selective response to global form in Glass patterns.