Luxotonic responses of units in macaque striate cortex

Abstract

1. Single units in striate cortex were studied in alert macaques while they viewed a ganzfeld. Of the 385 well-isolated units studied for 10 min to 2 h, 24% gave "luxotonic" responses, i.e., their rate of discharge for 1 min or more in diffuse, featureless, wideangle illumination (20-450 cd/m2) was at least double that during a comparable period in darkness, or vice versa, and not attributable to eye movements of blinking. Those discharging faster in the light, "photergic" units, outnumber those responding to darkness, "scotergic" units 1 by 4:1. 2. In the lateral geniculate nucleus, on the other hand, among 46 units studied, 28% were luxotonic, but scotergic units were the more common. Both types were present in both magno- and parvocellular laminae. 3. For striate cortex two-thirds of the luxotonic units were binocular. Some showed highly similar response for either eye alone, and essentially no summation binocularly; others had grossly differing responses from each eye, and complex binocular interaction. 4. Many units of all types at striate cortex showed significant modulation of their activity consequent to saccadic eye movements made in darkness, whereas comparable modulation was not observed at the lateral geniculate nucleus. 5. On the basis of these and other findings it is concluded that luxotonic cortical activity is prominent probably only in alert primates, and that this is a consequence of the fact that all retinal ganglion cells in primates synapse in the lateral geniculate nucleus (Ref. 9). Possible functions range from mere trophic input to providing a veridical image or a scaling factor for maintenance of perceptual constancy in the face of varying levels of general illumination.

Responses of human visual cortex to uniform surfaces

“…Such a finding places important constraints on possible physiological mechanisms for signaling the brightness of uniform surfaces. In monkey, the majority of neurons signaling surface luminance respond with either an increase or a decrease in firing to changes in luminance (photergic or scotergic, respectively) (6,7). The responses in human visual cortex we observed may therefore reflect the activation of two neuronal subpopulations homologous to those observed in monkey, signaling dark and light, respectively.…”

“…Theoretical accounts of surface perception have therefore often postulated a processing of ''filling in'' that mediates creation of surface representations at some level in the visual system (4,5). However, more recent reports suggest that some cells in primary visual cortex do indeed respond to the luminance of uniform surfaces (6)(7)(8)(9)(10). Furthermore, in humans there is a close relationship between perceived brightness contrast and responses in primary visual cortex (11)(12)(13)(14)(15), suggesting that other sensations of brightness may also be encoded in primary visual cortex.…”

Cortical processing of a brightness illusion

“…How the brain encodes such local and global brightness cues is unknown. Only a few studies have examined neuronal response to uniform surfaces (4)(5)(6)(7)(8)(9). These studies have shown that although cells modulated by luminance change are found as early as the retina and lateral geniculate nucleus (LGN), those modulated by perceived brightness change, which occur independent of actual luminance change over the receptive field (RF), can be found as early as the primary visual cortex (V1).…”

Neuromagnetic Correlates of Perceived Brightness in Human Visual Cortex

“…We found that the MEG response was better accounted for by log-scaled luminance (Table 1, middle) than was the physical luminance of the stimulus (Table 1, left). Some electrophysiological studies with non-human primates reported that the electrical activity of neurons in the primary visual cortex depends linearly on the logarithm of luminance (Kayama et al, 1979;Kinoshita & Komatsu, 2001). There are also a few fMRI and EEG studies of humans, which suggest that the activation intensity in the primary visual cortex is linearly dependent on the logarithm of luminance contrast (Avidan, Harel, Hendler, Ben-Bashat, Zohary, & Malach, 2002;Boynton, Demb, Glover, & Heeger, 1999;Goodyear & Menon, 1998;Souza, Gomes, Saito, Filho, & Silveira, 2007).…”

“…A few electrophysiological studies with non-human primates have reported that individual Correspondence concerning this article should be addressed to Aki Kondo, Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1, Komaba, Meguro-ku, Tokyo, 1538904, Japan, (email: kondo@fennel.rcast.u-tokyo.ac.jp). neurons exhibit a compressive dependency of discharge rate on luminance, and that neural activity depends linearly on the logarithm of luminance in the primary visual cortex (Kayama, Riso, Bartlett, & Doty, 1979;Kinoshita & Komatsu, 2001).…”