Spatial interactions in the rhesus monkey retina: a behavioural study using the Westheimer paradigm.

For two trained rhesus monkeys, increment thresholds for a small test-spot of 100 ms duration were determined as a function of background size, at 10 retinal eccentricities along the horizontal meridian. Typical 'Westheimer-functions' were obtained, i.e. threshold first increases with increasing background size, reaches a maximum, then decreases with further increasing backgrounds and finally reaches a plateau. With increasing retinal eccentricities, the position of the peak of the functions is shifted towards larger background sizes, indicating an increase of perceptive field centre size from 0.25 degrees at 5 degrees eccentricity to 1.5 degrees at 40 degrees eccentricity. The perceptive field centres tend to be slightly smaller in the nasal retina. Total perceptive field sizes, as indicated by the beginnings of the plateaus, increase from about 1 degree near the fovea to about 3 degrees at 40 degrees eccentricity. The perceptive field centre sizes of two human observers, tested under the same experimental conditions, closely resemble those of the monkeys. The total perceptive fields are larger in the human subjects. The retinal ganglion cells determining threshold in this experiment are most likely the broad-band cells. The agreement between the behaviourally determined perceptive field centre sizes and the receptive field centre sizes of broadband cells (measured by DeMonasterio and Gouras 1975) is excellent. The dendritic fields of P-alpha-ganglion cells, most likely the morphological substrates of the broad-band cells (Perry, Oehler and Cowey 1984) are somewhat smaller at all eccentricities.(ABSTRACT TRUNCATED AT 250 WORDS)