action asymmetry hypothesis

There is a well-documented phenomenon in perception: lower frequency information is processed faster in the right hemisphere, and higher frequency information is processed faster in the left hemisphere. This is true in both vision and audition.

Why? The action asymmetry hypothesis proposes that this comes from hand dominance. Your dominant hand performs fine motor actions (writing, threading a needle), which require high spatial frequency processing. Your non-dominant hand performs coarse motor actions (stabilizing, holding), which require low spatial frequency processing.

Because most people are right-handed, and motor cortex is contralateral (right hand controlled by left hemisphere), this would cause left hemisphere specialization for high frequencies and right hemisphere specialization for low frequencies.

Low frequency vs high frequency gratings

Fig. 1: Spatial frequency gratings. Low frequency (left) has wider bars, high frequency (right) has narrower bars. The brain processes these differently depending on which hemisphere receives the information.

Visual pathway showing contralateral processing

Fig. 2: The visual pathway is contralateral. Information from the left visual field (B) goes to the right hemisphere, and information from the right visual field (A) goes to the left hemisphere. This crossing happens at the optic chiasm.

Hemispheric specialization for spatial frequency

Fig. 3: The complete model. Global/low frequency information in the left visual field (LVF) is processed by the right hemisphere. Local/high frequency information in the right visual field (RVF) is processed by the left hemisphere. The H made of Ts illustrates global vs local processing.

research questions

Do right and left handers have systematically different frequency information in their left and right visual hemifields, as measured in egocentric video?

Do right handers have more high-frequency information in the right visual field, and left handers more high-frequency information in the left?

hypotheses

H1input asymmetry causes frequency specialization

H2ipsilateral connections between motor and parietal/perceptual cortex cause frequency specialization

methods

(1)model left and right hemifields based on gaze data

(2)quantify spatial and temporal frequency information in left and right hemifields

(3)compare left and right handers

what i did

I worked with egocentric eye gaze data, processing video recordings to extract gaze coordinates. Using Fourier transforms, I plotted out sections of high and low spatial frequency power across the left and right visual hemifields. This allowed us to quantify whether there were systematic differences in frequency content based on handedness.