Cross- and iso- oriented surrounds modulate the contrast response function: the effect of surround contrast

Area of Science:

• Visual perception
• Neuroscience
• Psychophysics

Background:

• Visual target detectability and appearance are influenced by surrounding visual elements.
• Understanding surround modulation is crucial for comprehending visual processing.

Purpose of the Study:

• To investigate how cross- and iso-oriented surrounds affect contrast detection and discrimination in foveal vision.
• To systematically measure Threshold-versus-Contrast (TvC) functions under varying pedestal and surround contrasts.

Main Methods:

• Systematic measurement of Threshold-versus-Contrast (TvC) functions.
• Controlled presentation of visual targets with varying pedestal and surround contrasts.
• Analysis of contrast detection and discrimination performance.

Main Results:

• Cross-oriented surrounds consistently reduced contrast detection thresholds across all tested conditions.
• Iso-oriented surrounds exhibited contrast-dependent modulation: facilitative when surround/pedestal contrast ratio was less than 1, and suppressive when greater than 1.
• Cross-surround facilitation was primarily attributed to improved neural gain, except at extreme surround contrasts.

Conclusions:

• Cross-oriented surrounds offer a consistent benefit to contrast detection, likely via enhanced gain.
• Iso-surround effects are complex, suggesting multiple underlying neural processes influenced by relative stimulus intensity.
• The findings provide insights into the mechanisms of surround modulation in human foveal vision.