Purchase this article with an account.
Po-Jang Hsieh, Gideon P. Caplovitz, Peter U. Tse; Neural correlates of conscious visibility found in ipsilateral retinotopic cortex. Journal of Vision 2005;5(8):224. doi: 10.1167/5.8.224.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Perceptual fading occurs when an object, though present in the world and casting light upon the retina, vanishes from visual consciousness. Perceptual fading may be caused by bottom-up local adaptation mechanisms that attenuate the edge signal sent to cortex by retinal ganglion cells under conditions of visual fixation. In addition, there may be a cortical component underlying perceptual fading because a “filling in” mechanism replaces the missing object information with that of the background. The event-related functional magnetic resonance imaging (fMRI; n=15) data reported here reveal that the BOLD signal in ventral retinotopic areas (V1, V2V, VP, and V4V, but not LGN, V2D, V3, V3A, or MT) decreases when an object subjectively disappears, and increases when the object reappears. Surprisingly, this effect occurs whether the stimulus is presented contralaterally or ipsilaterally. This modulation occurs on top of a negative BOLD response in V1/V2, suggesting modulation of an inhibitory signal that suppresses neural activity in ipsilateral and contralateral retinotopic areas. We conclude that there must be cortical signals involved in perceptual fading for three reasons: (1) Negative BOLD responses observed in the ipsilateral LGN must be due to a feedback signaling mechanism sent from the cortex; (2) Though there is a general decrease in BOLD signal response in the LGN, it does not modulate with perceptual state. Therefore, the neural correlates of perceptual fading presumably occur after the LGN, whether in V1 or elsewhere in cortex; (3) Since the object that fades does not project signal directly from the retina to ipsilateral V1, the ipsilateral effect implies that ipsilateral V1 is receiving feedback from either contralateral V1 or other cortical areas.
This PDF is available to Subscribers Only