Featural representation and internal noise underlie the eccentricity effect in contrast sensitivity

Area of Science:

• Neuroscience
• Vision Science
• Computational Neuroscience

Background:

• Human visual performance, including contrast sensitivity and acuity, is highest at the fovea and decreases with eccentricity.
• The underlying causes of the eccentricity effect, particularly the role of differential feature tuning versus internal noise, remain incompletely understood.

Approach:

• Investigated the eccentricity effect by examining featural representation (tuning) and internal noise in human observers.
• Employed psychophysical reverse correlation to estimate visual system weights for orientations and spatial frequencies (SFs) at foveal and perifoveal locations.
• Measured response consistency using a double-pass method to infer internal noise levels via a noisy observer model.

Key Points:

• Found higher sensitivity to task-relevant orientations and SFs at the fovea compared to the perifovea, with no difference in feature selectivity.
• Demonstrated lower internal noise at the fovea than in perifoveal vision.
• Observed correlations between individual contrast sensitivity, feature sensitivity/selectivity, and internal noise.

Conclusions:

• The behavioral eccentricity effect is primarily driven by the fovea's superior orientation sensitivity and reduced internal noise.
• Suggests that enhanced representation of task-relevant features and diminished internal noise in the fovea contribute significantly to the observed eccentricity effect in human vision.