Real and illusory contour processing in area V1 of the primate: A cortical balancing act

Benjamin M. Ramsden, Chou P. Hung, Anna Wang Roe

Research output: Contribution to journalArticlepeer-review

153 Scopus citations


It is known that neurons in area V2 (the second visual area) can signal the orientation of illusory contours in the primate. Whether area V1 (primary visual cortex) can signal illusory contour orientation is more controversial. While some electrophysiology studies have ruled out illusory signaling in V1, other reports suggest that V1 shows some illusory-specific response. Here, using optical imaging and single unit electrophysiology, we report that primate V1 does show an orientation-specific response to the 'abutting line grating' illusory contour. However, this response does not signal an illusory contour in the conventional sense. Rather, we find that illusory contour stimulation leads to an activation map that, after appropriate subtraction of real line signal, is inversely related to the real orientation map. The illusory contour orientation is thus negatively signaled or de-emphasized in V1. This 'activation reversal' is robust, is not due merely to presence of line ends, is not dependent on inducer orientation, and is not due to precise position of line end stimulation of V1 cells. These data suggest a resolution for previous apparently contradictory experimental findings. We propose that the de-emphasis of illusory contour orientation in V1 may be an important signal of contour identity and may, together with illusory signal from V2, provide a unique signature for illusory contour representation.

Original languageEnglish (US)
Pages (from-to)648-665
Number of pages18
JournalCerebral Cortex
Issue number7
StatePublished - 2001
Externally publishedYes

ASJC Scopus subject areas

  • Cognitive Neuroscience
  • Cellular and Molecular Neuroscience


Dive into the research topics of 'Real and illusory contour processing in area V1 of the primate: A cortical balancing act'. Together they form a unique fingerprint.

Cite this