Modulation Of Visual Sensitivity Research Articles

Visual sensitivity for luminance and chromatic stimuli during the execution of smooth pursuit and saccadic eye movements

Visual sensitivity is dynamically modulated by eye movements. During saccadic eye movements, sensitivity is reduced selectively for low-spatial frequency luminance stimuli and largely unaffected for high-spatial frequency luminance and chromatic stimuli (Nature 371 (1994), 511–513). During smooth pursuit eye movements, sensitivity for low-spatial frequency luminance stimuli is moderately reduced while sensitivity for chromatic and high-spatial frequency luminance stimuli is even increased (Nature Neuroscience, 11 (2008), 1211–1216). Since these effects are at least partly of different polarity, we investigated the combined effects of saccades and smooth pursuit on visual sensitivity. For the time course of chromatic sensitivity, we found that detection rates increased slightly around pursuit onset. During saccades to static and moving targets, detection rates dropped briefly before the saccade and reached a minimum at saccade onset. This reduction of chromatic sensitivity was present whenever a saccade was executed and it was not modified by subsequent pursuit. We also measured contrast sensitivity for flashed high- and low-spatial frequency luminance and chromatic stimuli during saccades and pursuit. During saccades, the reduction of contrast sensitivity was strongest for low-spatial frequency luminance stimuli (about 90%). However, a significant reduction was also present for chromatic stimuli (about 58%). Chromatic sensitivity was increased during smooth pursuit (about 12%). These results suggest that the modulation of visual sensitivity during saccades and smooth pursuit is more complex than previously assumed.

Fronto-tectal white matter connectivity mediates facilitatory effects of non-invasive neurostimulation on visual detection

The causal ability of pre-target FEF activity to modulate visual detection for perithreshold stimuli has been recently demonstrated in humans by means of non-invasive neurostimulation. Yet in spite of the network-distributed effects of these type of techniques, the white matter (WM) tracts and distant visual nodes contributing to such behavioral impact remain unknown. We hereby used individual data from a group of healthy human subjects, who received time-locked pulses of active or sham Transcranial Magnetic Stimulation (TMS) to the right Frontal Eye Field (FEF) region, and experienced increases in visual detection sensitivity. We then studied the extent to which interindividual differences in visual modulation might be dependent on the WM patterns linking the targeted area to other regions relevant for visuo-attentional behaviors. We report a statistically significant correlation between the probability of connection in a right fronto-tectal pathway (FEF-Superior Colliculus) and the modulation of visual sensitivity during a detection task. Our findings support the potential contribution of this pathway and the superior colliculus in the mediation of visual performance from frontal regions in humans. Furthermore, we also show the ability of a TMS/DTI correlational approach to contribute to the disambiguation of the specific long-range pathways driving network-wide neurostimulatory effects on behavior, anticipating their future role in guiding a more efficient use of focal neurostimulation.