Extrageniculostriate vision in the monkey. VII. Contrast sensitivity functions

Area of Science:

• Neuroscience
• Vision Science
• Psychophysics

Background:

• The striate cortex is crucial for processing spatial frequency, contrast, and orientation for pattern recognition.
• Monkeys with striate cortex ablation show residual pattern discrimination and can distinguish bar orientations.

Purpose of the Study:

• To investigate the spatial frequency detection capabilities of monkeys with bilateral striate cortex ablation.
• To assess the impact of contrast levels and maximum contrast (visual acuity) on this detection ability.

Main Methods:

• Monkeys performed a forced-choice task discriminating homogeneous targets from sinusoidal gratings at various spatial frequencies and contrasts.
• Contrast thresholds were measured using staircase and constant stimuli methods before and after striate cortex ablation.

Main Results:

• Normal monkeys discriminated all tested spatial frequencies; destriated monkeys could only discriminate frequencies between 0.5 and 4.0 cycles/deg.
• Contrast sensitivity functions showed a characteristic inverted J-shape, significantly depressed post-ablation with a 26-dB flat loss.
• High-frequency cutoff decreased from 43 cycles/deg preoperatively to 12 cycles/deg postoperatively, impacting visual acuity.

Conclusions:

• Destriated monkeys exhibit impaired, yet present, spatial frequency detection and contrast sensitivity.
• Ablation of the striate cortex leads to a significant reduction in visual processing capabilities, particularly at higher spatial frequencies.