Induced deficits in speed perception by transcranial magnetic stimulation of human cortical areas V5/MT+ and V3A.

In this report, we evaluate the role of visual areas responsive to motion in the human brain in the perception of stimulus speed. We first identified and localized V1, V3A, and V5/MT+ in individual participants on the basis of blood oxygenation level-dependent responses obtained in retinotopic mapping experiments and responses to moving gratings. Repetitive transcranial magnetic stimulation (rTMS) was then used to disrupt the normal functioning of the previously localized visual areas in each participant.

Extrafoveal viewing reveals the nature of second-order human vision.

For the majority of visual tasks, performance in extrafoveal vision can be equated with that at the fovea simply by a change in spatial scale of the stimuli (magnification). We sought to exploit this association to examine the nature of second-order vision. More specifically, we investigate the relationship between the scale of second-order vision and the scale of its first-order input.

Functional evidence for cone-specific connectivity in the human retina.

Physiological studies of colour vision have not yet resolved the controversial issue of how chromatic opponency is constructed at a neuronal level. Two competing theories, the cone-selective hypothesis and the random-wiring hypothesis, are currently equivocal to the architecture of the primate retina. In central vision, both schemes are capable of producing colour opponency due to the fact that receptive field centres receive input from a single bipolar cell - the so called 'private line arrangement'.

Positional adaptation reveals multiple chromatic mechanisms in human vision.

Precortical color vision is mediated by three independent opponent or cardinal mechanisms that linearly combine receptoral outputs to form L/M, S/(L+M), and L+M channels. However, data from a variety of psychophysical and physiological experiments indicate that chromatic processing undergoes a reorganization away from the basic opponent model. Frequently, this post-opponent reorganization is viewed in terms of the generation of multiple "higher order" chromatic mechanisms, tuned to a wide variety of axes in color space.