Decreasing visual subitising performance with age

Abstract

Subitising, the ability to quickly and intuitively enumerate small numbers of items, is likely to be mediated by parallel processing. The purpose of our study was to ask whether visual subitising performance changes with age. We recruited 17 “junior” observers (21–30 years), and 14 “senior” observers (60–85 years). All had normal visual acuity. On each trial, a number (N) of black circular dots was presented on the monitor screen for 200 ms against a gray background (40 cd/m²). N ranged from 1–10 dots; the dots were randomly positioned in a 10 x 10 square (1 deg x 1 deg). Observers were asked to enumerate the number of dots as quickly and accurately as they could. Response latency was measured using the time it took to say the number into a microphone. The mean subitising thresholds were 7.08±0.30 and 4.73±0.36 dots for the junior and senior age groups, respectively. There was a statistically significant difference between the two means (unpaired t=5.08; df=30; p<0.0001). Response latencies for the stimuli up to 7 dots were about the same in both groups. Latencies were about 500 ms for 1 to 3 dots, and thereafter increased linearly at the rate of about 300 ms/dot. We found that the subitising performance deteriorates with advancing age. Control experiments using artificial pupils and reduced stimulus luminance show that subitising losses cannot be explained by the optical changes or by reduced retinal illuminance. Our findings support the hypothesis that parallel processing may be affected by age.