Dorsal and ventral visual stream contributions to perception-action interactions during pointing

Area of Science:

• Neuroscience
• Cognitive Psychology
• Visual Perception

Background:

• The Ebbinghaus illusion demonstrates how perceived object size influences motor behavior.
• Previous research suggests potential roles for both ventral (object size) and dorsal (sensorimotor) visual streams in this effect.

Purpose of the Study:

• To investigate the specific roles of the ventral and dorsal visual streams in mediating the Ebbinghaus illusion's effect on pointing movements.
• To differentiate between direct dorsal stream involvement and ventral stream contributions via prefrontal pathways.

Main Methods:

• Transcranial magnetic stimulation (TMS) was used to transiently disrupt processing in the ventral stream, dorsal stream, or a control area (SMA).
• Participants performed pointing movements towards targets within the Ebbinghaus illusion display.
• Reaction time, movement speed, and accuracy were measured under different TMS conditions.

Main Results:

• Disrupting either the dorsal or ventral stream with TMS reduced the illusion's impact on pointing movement speed.
• However, a control experiment revealed that only dorsal stream disruption maintained the effect on movement speed when physical size, not relative size, was manipulated.
• Neither TMS over the dorsal nor ventral stream affected reaction time or movement accuracy.

Conclusions:

• The ventral stream, through projections to prefrontal cortex, contributes to visually guided pointing based on relative size information.
• The dorsal stream's role appears less critical for this specific illusion's impact on pointing speed when relative size is the primary cue.