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

Area of Science:

• Neuroscience
• Vision Science
• Ophthalmology

Background:

• Understanding the spatial properties of visual perception is essential for comprehending retinal processing.
• The relationship between background size and visual detection thresholds (Westheimer functions) provides insights into receptive field organization.

Purpose of the Study:

• To determine increment thresholds as a function of background size across various retinal eccentricities in rhesus monkeys.
• To compare the visual perceptive field characteristics of monkeys with those of human observers.
• To investigate the neural basis of these visual phenomena by relating behavioral data to retinal ganglion cell properties.

Main Methods:

• Increment thresholds were measured for a small test spot in two trained rhesus monkeys at 10 retinal eccentricities along the horizontal meridian.
• Westheimer functions were generated by varying background size.
• Perceptive field center and total perceptive field sizes were calculated from these functions.
• Human observers were tested under identical experimental conditions for comparison.

Main Results:

• Typical Westheimer functions were observed, characterized by an initial increase, peak, decrease, and plateau in threshold with increasing background size.
• Perceptive field center size increased with retinal eccentricity in monkeys, from 0.25 degrees at 5 degrees eccentricity to 1.5 degrees at 40 degrees eccentricity.
• Total perceptive field size increased from approximately 1 degree near the fovea to 3 degrees at 40 degrees eccentricity.
• Monkey and human perceptive field center sizes were comparable, though human total perceptive fields were larger.

Conclusions:

• Behaviorally determined perceptive field center sizes in monkeys closely match the receptive field center sizes of broadband retinal ganglion cells.
• This suggests that broadband cells are the primary determinants of visual thresholds in this paradigm.
• The findings provide strong evidence for the role of specific retinal cell types in shaping visual perception across the retina.