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Abstract:
There is a strong body of evidence that the magno-cellular pathway (MC)
dominates the lower visual fi eld (LVF); nevertheless there is no clear evidence,
so far, if the upper visual fi eld (UVF) is dominated by the parvo-cellular
pathway (PC). This study was aimed to investigate, using simple reaction
times (RTs), the contribution of MC and PC pathways on LVF and UVF. Ten
participants from the Max Planck Institute for Biological Cybernetics Subject’s
Database, all of them with normal color vision, took part in this study. Two
experiments were performed in a colored calibrated monitor and color
coordinates were measured with a PR-650 SpectraScan Colorimeter (Photo
Research, Inc.). In the two experiments, subjects pressed a response key to the
onset of the target (RTs), a dot subtending 1° of visual angle, briefl y presented
(150ms) on a grid of 82 different positions (covering an area of 24° by 16°) on
the computer screen. Participants were asked to always fi xate their gaze to
a fi xation cross located to the center of the screen and eye movements were
monitored with an eye tracker (EyeLink II - SR Research Ltd). In experiment
I, a white dot (CIE x, y = 0.313, 0.329) with a luminance of 80 cd/m2 was
presented against a black background. In the fi rst phase of experiment II,
heterochromatic fl icker photometry was used for every participant to reach
isoluminance of the target and background, using a green dot (CIE x,y = 0.212,
0.260) presented against a red background (CIE x, y = 0.360, 0.260). Results
from experiment I confi rm previous fi ndings of a MC advantage on the LVF
(319±15ms) against UVF (332±9ms) (T= 4.52, p< 0.0001). Experiment II showed, instead, a PC facilitation on the UVF (350±17ms) when compared to the LVF
(362±20ms) (T= 2.96, p= 0.004). In conclusion, with this simple and classical
approach (RTs) it was possible to demonstrate the different contribution from
each pathway to LVF and UVF.
