Stimulus magnification equates identification and discrimination of biological motion across the visual field.
There is conflicting evidence about whether stimulus magnification is sufficient to equate the discriminability of point-light walkers across the visual field. We measured the accuracy with which observers could report the directions of point-light walkers moving +/-4 degrees from the line of sight, and the accuracy with which they could identify five different point-light walkers. In both cases accuracy was measured over a sevenfold range of sizes at eccentricities from 0 degrees to 16 degrees in the right visual field. In most cases observers (N=6) achieved 100% accuracy at the largest stimulus sizes (20 degrees height) at all eccentricities. In both tasks the psychometric functions at each eccentricity were shifted versions of each other on a log-size axis. Therefore, by dividing stimulus size at each eccentricity (E) by an appropriate F=1+E/E(2) (where E(2) represents the eccentricity at which stimulus size must double to achieve equivalent-to-foveal performance) all data could be fit with a single function. The average E(2) value was .91 (SEM=.19, N=6) in the walker-direction discrimination task and 1.34 (SEM=.21, N=6) in the walker identification task. We conclude that size scaling is sufficient to equate discrimination and identification of point-light walkers across the visual field.
Gurnsey
Rick
R
Department of Psychology, Concordia University, 7141 Sherbrooke Street West, Montreal, Que., Canada H4B 1R6. Rick.Gurnsey@concordia.ca
Roddy
Gabrielle
G
Ouhnana
Marouane
M
Troje
Nikolaus F
NF
D000328:Adult; D004192:Discrimination, Psychological; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009039:Motion Perception / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D011601:Psychophysics; D012684:Sensory Thresholds / Q000502:physiology; D014794:Visual Fields / Q000502:physiology*; D055815:Young Adult