Chromatic Effects on V1 and V2 Currents

Color has a varied affect on the visual system. Magno cells respond well to luminance contrast, but poorly to color only differences. Parvo cells are less sensitive to luminance contrast, but respond well to chromatic differences due to their spectral opponency, (Livingstone and Hubel, 1987, 1988). While Magno cells are considered to be “color-blind” (Livingstone and Hubel, 1987, 1988), Logothetis et al. (1990) showed in rhesus monkey single-cell recordings that LGN Magno cells continue to respond at a reduced rate to isoluminance, thus potentially still providing information to the system.

Wiesel and Hubel (1966) found a large proportion of Magno pathway cells are inhibited by red light. The tonic suppression of Magno pathway firing caused by red light has been demonstrated in monkey retinal ganglion cells (de Monasterio, 1978), the LGN (Dreher et al., 1976; Kruger, 1977; Wiesel and Hubel, 1966), and the striate cortex (Livingstone and Hubel, 1984). Red suppression has not been confirmed physiologically in humans, however, evidence is consistent for the red effect psychophysically using red backgrounds in psychophysical and behavioral tasks (Breitmeyer and Breier, 1994; Brown and Koch, 2000; Cavanagh et al., 1984; Rudvin and Valberg, 2006; Rudvin et al., 2000; Rudvin, 2005; Klistorner et al., 1997; Bedwell et al., 2003; Breitmeyer and Williams, 1990; Edwards et al., 1996). Skottun (2004) notes conclusions must be made carefully to the effects of red stimuli as red also affects parvocellular red–green color-opponent cells, thus, changes measured as a result of red light are not exclusively from suppressing the Magno pathway. In addition, Givre et al. (1995) showed a larger V1 response to red flashes compared to blue and green in macaque single-cell recording.

This study investigates chromatic effects on V1 and V2 currents in humans. Luminance contrast and isoluminant PPmfVEP dartboard stimuli are used with permutations of red, green, and gray checks and backgrounds.

Inverso, S. A. “Evoked Currents in Human Visual Cortex.” (PhD Dissertation) The Australian National University, Canberra, ACT, AU (2010).

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