Stronger occipital cortical activation to lower than upper visual field stimuli

Abstract

We recorded whole-scalp magnetoencephalographic (MEG) responses to black-and-white checkerboards to study whether the human cortical responses are quantitatively similar to stimulation of the lower and upper visual field at small, 0-6 degrees, eccentricities. All stimuli evoked strong occipital responses peaking at 50-100 ms (mean 75 ms). The activation was modeled with a single equivalent current dipole in the contralateral occipital cortex, close to the calcarine fissure, agreeing with an activation of the V1/V2 cortex. The dipole was, on average, twice as strong to lower than to upper field stimuli. Responses to hemifield stimuli that extended to both lower and upper fields resembled the responses to lower field stimuli in source current direction and strength. These results agree with psychophysical data, which indicate lower visual field advantage in complex visual processing. Parieto-occipital responses in the putative V6 complex were similar to lower and upper field stimuli.

Spatial Anisotropy of Saccadic Latency in Normal Subjects and Brain-Damaged Patients

“…The longer latency for saccades towards the lower targets is also in contrast with findings in other kinds of tasks. Indeed, lower-visual field advantage has been also observed for temporal and spatial contrast sensitivity (e.g., Skrandies, 1985aSkrandies, , 1985b, visual acuity (Millodot and Lamont, 1974), motor reaction time (e.g., Payne, 1967), visual evoked potentials latencies (Lehmann and Skrandies, 1979;Skrandies, 1987;Rudell et al, 1993;Pitzalis et al, 1997) and functional activation (Portin et al, 1999). Differences in the processing of the upper and lower retinal visual stimuli could be explained by a general superiority of the upper over the lower hemiretinal system.…”

Keep looking ahead? Re-direction of visual fixation does not always occur during an unpredictable obstacle avoidance task

“…In humans, the density of ganglion cells in the superior hemiretina is 60% greater than the inferior hemiretina suggesting a processing bias for visual stimuli in the lower visual Weld (Curcio and Allen 1990). Furthermore, Portin et al (1999) using magnetoencephalography have reported stronger cortical activations in the calcarine Wssure of the occipital cortex from visual stimuli in the lower visual Weld. Thus, we are particularly suited to utilize visual information obtained from the periphery in the lower visual Weld.…”

Neural correlates of perceptual filling-in of an artificial scotoma in humans

“…This frequency was chosen because it produces the largest amplitude oscillatory MEG signal (38). The lower half of the visual field was chosen for placement of the target, because filling-in has been shown to be more robust (9) and because MEG signals have been shown to be stronger for stimuli presented in the lower visual field (39). In behavioral experiments before scanning, we confirmed that the target was small enough to allow filling-in to occur, despite the pertinent flickering, but large enough to detect by using steady-state MEG responses.…”