Unilateral hemispheric activation does not affect free-viewing perceptual asymmetries

Area of Science:

• Cognitive Psychology
• Neuroscience
• Visual Perception

Background:

• A significant leftward bias exists when selecting the darker of two mirror-reversed luminance gradients in free viewing.
• This bias suggests an asymmetry in visual processing, potentially influenced by hemispheric dominance.

Purpose of the Study:

• To investigate whether unilateral hemispheric activation influences the leftward perceptual bias for luminance gradients.
• To determine if manipulating activation through motor tasks affects visual processing asymmetries.

Main Methods:

• Two experiments were conducted with right-handed participants (N=52 and N=24).
• Experiment 1 involved unilateral activation via left or right finger tapping.
• Experiment 2 involved unilateral activation via left or right hand clenching.

Main Results:

• Participants consistently selected the left-sided darker stimulus 73% of the time.
• Neither finger tapping nor hand clenching significantly altered the leftward perceptual bias.
• Activation strength and hemispace manipulation did not impact the observed asymmetry.

Conclusions:

• Unilateral hemispheric activation, induced by motor tasks, does not modulate the leftward bias in luminance gradient perception.
• The consistent leftward bias suggests that factors other than immediate hemispheric activation, such as scanning biases, may underlie this perceptual asymmetry.