Sensitivity to first- and second-order drifting gratings in 3-month-old infants

Abstract

In two experiments, we investigated 3-month-old infants' sensitivity to first- and second-order drifting gratings. In Experiment 1 we used forced-choice preferential looking with drifting versus stationary gratings to estimate depth modulation thresholds for 3-month-old infants and a similar task for a comparison group of adults. Thresholds for infants were more adult-like for second-order than first-order gratings. In Experiment 2, 3-month-olds dishabituated to a change in first-order orientation, but not to a change in direction of first- or second-order motion. Hence, results from Experiment 1 were likely driven by the perception of flicker rather than motion. Thus, infants' sensitivity to uniform motion is slow to develop and appears to be driven initially by flicker-sensitive mechanisms. The underlying mechanisms have more mature tuning for second-order than for first-order information.

Keywords: Development; first-order; flicker; infants; motion; second-order.

Figure 1.

Experimeter's accuracy (mean percent of correct responses (±1 s.e) based on 3-month-olds' responses to moving versus stationary (a) first-order gratings and (b) second-order gratings. The 50% value on the y-axis represents performance expected by chance. Values marked with an asterisk indicate values that are significantly above chance (p < .0.125). Note that the values on the x-axes (log luminance- or contrast-modulation) cannot be compared directly because they are in units relevant to two different properties (change in luminance versus in contrast, respectively).

Figure 2.

infants' estimated log thresholds and adults' mean log thresholds for luminance-modulated (LM) and contrast-modulated (CM) stimuli. Error bars denote the estimated range of the threshold for infants and standard error of the mean for adults. On a log scale, negative values represent modulations lower than 1%.

Figure 3.

Three-month-olds' looking times (±1 s.e) during the test phase after habituation to vertical gratings moving leftward or rightward. Results are for vertical gratings moving in the habituated direction, vertical gratings moving in a novel opposite direction, and horizontal gratings moving downward (both a novel orientation and direction of motion) for (a) first-order and (b) second-order motion. infants' looking times did not differ for the novel versus habituated direction of motion. However, infants did look significantly longer at the grating with novel orientation than the habituated orientation, but only when tested with first-order stimuli.