Abstract
BACKGROUND:
The question of whether infants can use one visual feature developmentally before another can only be studied legitimately if manipulations to those features are equally salient (Kaldy, Blaser, & Leslie, 2006). Our ‘Interdimensional Salience Mapping’ method allowed us to generate three comparison objects whose salience difference from a common baseline object was equal along one of three feature dimensions: shape, luminance or color. We then compared infants' visual working memory (VWM) for these features.
METHODS:
General: Age range: 8;15 – 9;15 (Exp. 1: n=14, Exp. 2: n=22). All stimuli were presented on a 21″ LCD monitor.
Experiment 1: Salience differences were calibrated by pitting a baseline object (a yellow geometric figure) against another object that differed from the baseline either in shape, luminance or color (red saturation) in a preferential looking paradigm. (For shape, we varied perimeter, while keeping area constant.) Gaze direction (left/right) was coded. Data from 14 subjects yielded monotonically increasing psychometric functions of feature ‘intensity’ versus preference. Values at the 67% preference level were chosen; objects with these values have iso-salient differences from baseline along their respective feature dimensions.
Experiment 2: We used the violation-of-expectation method. Infants saw one of the objects in the baseline-comparison object pair, which was occluded for 2 seconds, and then either the same object or the other object in the pair was revealed. Looking times were measured.
RESULTS:
Using the iso-salient stimuli from Experiment 1, we found that 9-month-olds were able to maintain shape information in VWM. The luminance and the color tests are currently ongoing, but preliminary results show that infants note color changes, but not luminance.
DISCUSSION:
‘Interdimensional Salience Mapping’ can generate psychophysically comparable stimuli. VWM results so far are consistent with our “Ecological Memory” hypothesis, which predicts that reliable features of objects are better remembered.