Cite as:
Kojima H, Donnelly M, Lappin J S, 1998, "Acuity for relative motion is better than acuity for detecting absolute motion" Perception 27 ECVP Abstract Supplement

Acuity for relative motion is better than acuity for detecting absolute motion

H Kojima, M Donnelly, J S Lappin

Visual acuity for small movements is known to be better than that for small positional differences. We have found similar hyperacuities for detecting differences in the relative motions of spatially separated features.

Using three collinear Gaussian blobs (SD=10 min of arc) separated by 100 min of arc, we measured acuities in three types of tasks. Position acuity was measured in a static bisection task, with the central blob displaced slightly from the centre position defined by the two outer blobs. Absolute-motion acuity was measured as the smallest detectable amplitude of phase-locked sinusoidal oscillations of the blob positions. Relative-motion acuity was measured by moving the central blob antiphase to the outer blobs.

Positional acuities ranged from 40 to 53 s of arc. Absolute-motion thresholds were 17% to 30% of position thresholds, ranging from 9 to 12 s of arc. Relative-motion thresholds were lower still, ranging from 6 to 10 s of arc.

This demonstrates that the visual system is exquisitely sensitive to the relative motion of spatially separate image features. Also, relative-motion thresholds seem to remain low over increases in spatial separation and temporal frequencies of feature movement.

[Supported by NIH grants T32EY07135, P30EY08126, and a JSPS Research Fellowship for Young Scientists for HK.]

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