Perception of line orientation in the center and periphery of the visual field.

Perception of orientation in the center and periphery of the visual field were compared. The stimuli were bright lines 1 degree long. They were presented equiprobably in 18 orientations from 0 degree to 180 degrees at the center or at 20 degrees in the periphery of the visual field. Stimulus duration was 50 msec and its intensity was twice above the detection threshold for each localization. Percentage of errors, response standard deviation, stimulus standard deviation from the orientation assigned and information transmitted were studied. No scale or standard stimulus were presented. At both stimulus localizations the accuracy of orientation was high and the errors larger than 20 degrees were less than 10% of all responses. There was a small but significant foveal superiority in accuracy and information transmitted. For central vision, the percentage of errors, response standard deviation and stimulus standard deviation all showed an oblique effect, i. e. a lower performance with oblique lines than with vertical or horizontal. For the peripheral vision, some measures (response standard deviation) showed an oblique effect and others (stimulus standard deviation and percentage of errors) did not. This makes difficult the conclusions about the presence of an oblique effect at the periphery. Further studies by methods free of response bias are necessary.