Retinal eccentricity effects on reaction time to imagined stimuli

Area of Science:

• Neuroscience
• Cognitive Psychology
• Visual Perception

Background:

• Visual imagery, the ability to mentally visualize stimuli, is thought to rely on neural mechanisms shared with visual perception.
• Understanding the neural basis of visual imagery can provide insights into the functional organization of the visual cortex.

Purpose of the Study:

• To investigate the neural substrate of visual imagery by comparing reaction times (RT) to real and imagined visual stimuli.
• To determine if the visuotopic organization observed in visual perception is also present in visual imagery.

Main Methods:

• Tested normal participants and one patient with hemianopic visual field loss on simple reaction time (RT) tasks.
• Participants detected luminous squares presented at different retinal eccentricities and sizes, both visually and in imagination.
• Compared RT differences for central versus peripheral stimuli and for stimuli of varying sizes.

Main Results:

• Normal participants exhibited an eccentricity effect (slower RT for peripheral stimuli) for both real and imagined stimuli, similar to known effects in visual perception.
• The hemianopic patient, despite intact imagery in the affected hemifield, did not show the eccentricity effect in that field, unlike her intact side.
• Larger stimulus size led to faster RTs for both real and imagined stimuli in normal participants.

Conclusions:

• Visual perception and imagination share a common visuotopic organization.
• This shared organization is disrupted following deafferentation of the visual cortex, as evidenced by the hemianopic patient's results.
• The findings support the hypothesis that visual imagery involves the activation of early visual processing areas.