12328.full.pdf (740.86 kB)
Download file

Phase-Dependent Interactions in Visual Cortex to Combinations of First- and Second-Order Stimuli.

Download (740.86 kB)
journal contribution
posted on 14.12.2016, 16:13 by Claire V. Hutchinson, T. Ledgeway, C. L. Baker
A fundamental task of the visual system is to extract figure-ground boundaries between objects, which are often defined, not only by differences in luminance, but also by "second-order" contrast or texture differences. Responses of cortical neurons to both first- and second-order patterns have been studied extensively, but only for responses to either type of stimulus in isolation. Here, we examined responses of visual cortex neurons to the spatial relationship between superimposed periodic luminance modulation (LM) and contrast modulation (CM) stimuli, the contrasts of which were adjusted to give equated responses when presented alone. Extracellular single-unit recordings were made in area 18 of the cat, the neurons of which show responses to CM and LM stimuli very similar to those in primate area V2 (Li et al., 2014). Most neurons showed a significant dependence on the relative phase of the combined LM and CM patterns, with a clear overall optimal response when they were approximately phase aligned. The degree of this phase preference, and the contributions of suppressive and/or facilitatory interactions, varied considerably from one neuron to another. Such phase-dependent and phase-invariant responses were evident in both simple- and complex-type cells. These results place important constraints on any future model of the underlying neural circuitry for second-order responses. The diversity in the degree of phase dependence between LM and CM stimuli that we observed could help to disambiguate different kinds of boundaries in natural scenes. SIGNIFICANCE STATEMENT: Many visual cortex neurons exhibit orientation-selective responses to boundaries defined by differences either in luminance or in texture contrast. Previous studies have examined responses to either type of boundary in isolation, but here we measured systematically responses of cortical neurons to the spatial relationship between superimposed periodic luminance-modulated (LM) and contrast-modulated (CM) stimuli with contrasts adjusted to give equated responses. We demonstrate that neuronal responses to these compound stimuli are highly dependent on the relative phase between the LM and CM components. Diversity in the degree of such phase dependence could help to disambiguate different kinds of boundaries in natural scenes, for example, those arising from surface reflectance changes or from illumination gradients such as shading or shadows.

Funding

This work was supported by the Canadian Institutes of Health Research (Operating Grants MOP-119498 and MOP-9685 to C.B.). C.V.H was supported in part by a Human Frontier Science Program Organization Short-Term Fellowship. We thank Lynda Domazet, Guangxing Li, and Vargha Talebi for assistance with some of the experiments.

History

Citation

Journal of Neuroscience, 2016, 36 (49), pp. 12328-12337

Author affiliation

/Organisation/COLLEGE OF MEDICINE, BIOLOGICAL SCIENCES AND PSYCHOLOGY/MBSP Non-Medical Departments/Neuroscience, Psychology and Behaviour

Version

VoR (Version of Record)

Published in

Journal of Neuroscience

Publisher

Society for Neuroscience

issn

0270-6474

eissn

1529-2401

Acceptance date

11/10/2016

Copyright date

2016

Available date

07/06/2017

Publisher version

http://www.jneurosci.org/content/36/49/12328

Notes

Six month embargo

Language

en