How selective are V1 cells for pop-out stimuli?
Many neurons in visual area V1 respond better to a pop-out stimulus, such as a single vertical bar among many horizontal bars, than to a homogeneous stimulus, such as a stimulus with all vertical bars. Many studies have suggested such cells represent neural correlates of pop-out, or more generally figure-ground segregation. However, preference for pop-out stimuli over homogeneous stimuli could also arise from a nonspecific selectivity for feature discontinuities between the target and the background, without any specificity for pop-out per se. To distinguish between these two confounding scenarios, we compared the responses of V1 neurons to pop-out stimuli with the responses to "conjunction-target" stimuli, which have more complex feature discontinuities between the target and the surround, as in a stimulus with a blue vertical bar among blue horizontal bars and yellow vertical bars. The target in conjunction-target stimuli does not pop out, which we psychophysically verified. V1 cells in general responded similarly to pop-out and conjunction-target stimuli, and only a small minority of cells (approximately 2% by one measure) distinguished the pop-out and conjunction-target stimuli from each other and from homogeneous stimuli. Nevertheless, the responses of approximately 50% of the cells were significantly modulated across all center-surround stimuli, indicating that V1 cells can convey information about the feature discontinuities between the center and the surround as part of a network of neurons, although individual cells by themselves fail to explicitly represent pop-out. In light of our results, unambiguous pop-out selectivity at the level of individual cells remains to be demonstrated in V1 or elsewhere in the visual cortex.
Hegdé
Jay
J
Department of Neurobiology and Anatomy, University of Texas Medical School, Houston, Texas 77030, USA. jay@salk.edu
Felleman
Daniel J
DJ
D000818:Animals; D016000:Cluster Analysis; D015350:Contrast Sensitivity / Q000502:physiology; D005260:Female; D005364:Field Dependence-Independence; D005403:Fixation, Ocular / Q000502:physiology; D005556:Form Perception / Q000502:physiology; D008253:Macaca mulatta; D008297:Male; D009474:Neurons / Q000502:physiology; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D011930:Reaction Time / Q000502:physiology; D012815:Signal Processing, Computer-Assisted; D014793:Visual Cortex / Q000166:cytology / Q000502:physiology*