Age-related changes in motion direction discrimination in the horizontal plane

摘要

Motion perception, including determining the speed and direction of motion, has been found to deteriorate dramatically during healthy ageing. However, the extent to which ageing affects the discrimination of different motion directions is still unknown. Here, we investigated age-related changes in discriminating the direction of vertical and horizontal motion using random-dot kinematograms (RDK). In a first step, older (N = 16, 60 years) and younger adults (N = 27, 18-30 years) had to discriminate left/right (horizontal), or up/down (vertical) motion, with motion coherence at 100%. We determined stimulus duration individually for each participant with a minimum duration of 400ms. Stimulus durations did not differ significantly between age groups or motion directions. In a second step, using the same task with individually determined stimulus durations from step one, we measured motion coherence thresholds using the method of constant stimuli with stimulus coherences varying between 1% and 80%. Coherence thresholds did not differ significantly between groups but were significantly higher overall for vertical motion. In a third step, using individually determined stimulus durations and motion coherences, participants had to discriminate motion directions in a two-alternative forced-choice paradigm. Two RDKs were presented successively. In one RDK, dots moved either horizontally (right, 0?°) or vertically (up, 90?°), in the other RDK, dots moved diagonally between 1?° to 25?° degrees away from horizontal or vertical. Participants had to determine in which of the two RDKs the dots moved diagonally. Overall, accuracy improved with increasing angular deviations and was significantly higher in the vertical than the horizontal plane. Most interestingly however, older adultsa?? performance dramatically deteriorated in the horizontal plane, whereas their performance in the vertical plane was similar to younger adults. These results show that healthy ageing differentially affects motion direction discrimination along the vertical and horizontal planes.