Infants’ speed discrimination: Effects of different ratios and spatial orientations

The present study addressed the question whether 6-month-olds’ speed discrimination is ratio-dependent and whether an oblique effect (i.e., more accurate discrimination of cardinally as opposed to obliquely oriented objects) affects their speed discrimination skills. Infants were habituated to visual displays showing a ball moving with constant speed and tested with the familiar and a novel speed in the test phase. This ball moved either on a cardinally or obliquely oriented trajectory. Irrespective of orientation, infants looked longer at the novel speed when speeds differed by a ratio of 1:2, whereas they looked indiscriminably at the novel and familiar speeds when they differed by a ratio of 2:3. Our results show remarkable parallels to infants’ ratio-dependent discrimination behavior in other domains (time, distance, and number), implying that different magnitudes may be processed by the same underlying mechanism. However, our findings also indicate that speed discrimination was not influenced by spatial orientation in a similar way as has been found for other visual perceptual processes.