Two temporal channels in human V1 identified using fMRI

Abstract

Human visual sensitivity to a fairly broad class of dynamic stimuli can be modeled accurately using two temporal channels. Here, we analyze fMRI measurements of the temporal step response to spatially uniform stimuli to estimate these channels in human primary visual cortex (V1). In agreement with the psychophysical literature, the V1 fMRI temporal responses are modeled accurately as a mixture of two (transient and sustained) channels. We derive estimates of the relative contributions from these two channels at a range of eccentricities. We find that all portions of V1 contain a significant transient response. The central visual field representation includes a significant sustained response, but the amplitude of the sustained channel signal declines with eccentricity. The sustained signals may reflect the emphasis on pattern recognition and color in the central visual field; the dominant transient response in the visual periphery may reflect responses in the human visual attention system.

Early Suppressive Mechanisms and the Negative Blood Oxygenation Level-Dependent Response in Human Visual Cortex

“…Another explanation is that the parafovea may be more sensitive to the rapid flicker of our fluorescent monitor backlight. While some cells in macaque visual cortex can follow flicker up to a frequency of 100Hz (Williams, Mechler et al 2004; Logothetis, Murayama et al 2009) and the periphery is certainly more sensitive to high frequency flicker than the fovea (McKee and Taylor 1984; Tyler and Hamer 1990; Tyler and Hamer 1993; Horiguchi, Nakadomari et al 2009), the degree of entrainment is far higher when spatial contrast is present. Using a photocell and oscilloscope, we measured almost zero flicker in our LCD display below 100Hz during a mean field and we believe that it is unlikely that the small neural population that may be entrained (although not necessarily driven to spike more) above this frequency could drive the large offsets in BOLD signal that we observe.…”

Perception of differences in naturalistic dynamic scenes, and a V1-based model

“…These results seem to be consistent with the ''classical'' view of sustained and transient channels (a.k.a. the parvocellular vs. magnocellular processing pathways) with their different spatial frequency ranges (Hess & Snowden, 1992;Horiguchi et al, 2009;Keesey, 1972;Kulikowski & Tolhurst, 1973;Tolhurst, 1973Tolhurst, , 1975. In order to get good predictions of observers' ratings, it was necessary to have a multilinear regression that included both sustained and transient contributions.…”

“…One hypothesis has it that, in the early stages of the visual system, there are two parallel pathways. The transient or magnocellular (M-cell) pathway acts primarily on low spatial frequencies while the sustained or parvocellular (Pcell) pathway acts primarily on middle and high spatial frequencies (Derrington & Lennie, 1984;Gouras, 1968;Hess & Snowden, 1992;Horiguchi, Nakadomari, Misaki, & Wandell, 2009;Keesey, 1972;Kulikowski & Tolhurst, 1973;Tolhurst, 1973Tolhurst, , 1975. The two pathways have been proposed to convey different perceptual information about temporal and spatial structure (Keesey, 1972;Kulikowski & Tolhurst, 1973;Tolhurst, 1973).…”

Functional MRI Dynamics

“…Uludag had shown that these transients are mostly positive and can be observed as sole response in a voxel or can overlap with positive or negative sustained responses. Based on the observation of sustained and phasic responses in the visual cortex, Horiguchi et al had suggested that there are two parallel temporal streams of visual processing (Horiguchi, Nakadomari, Misaki, & Wandell, 2009). Based on the observation of sustained and phasic responses in the visual cortex, Horiguchi et al had suggested that there are two parallel temporal streams of visual processing (Horiguchi, Nakadomari, Misaki, & Wandell, 2009).…”