Babies and brains: habituation in infant cognition and functional neuroimaging

Abstract

Many prominent studies of infant cognition over the past two decades have relied on the fact that infants habituate to repeated stimuli - i.e. that their looking times tend to decline upon repeated stimulus presentations. This phenomenon had been exploited to reveal a great deal about the minds of preverbal infants. Many prominent studies of the neural bases of adult cognition over the past decade have relied on the fact that brain regions habituate to repeated stimuli - i.e. that the hemodynamic responses observed in fMRI tend to decline upon repeated stimulus presentations. This phenomenon has been exploited to reveal a great deal about the neural mechanisms of perception and cognition. Similarities in the mechanics of these two forms of habituation suggest that it may be useful to relate them to each other. Here we outline this analogy, explore its nuances, and highlight some ways in which the study of habituation in functional neuroimaging could yield novel insights into the nature of habituation in infant cognition - and vice versa.

Keywords: cognitive neuroscience; fMRI adaptation; implicit memory; novelty preferences; priming; repetition attenuation; repetition enhancement; repetition suppression.

Figure 1

An example of habituation in infant cognition (adapted from Baillargeon, 1987). (A) Side view of habituation and test displays. In both conditions, infants were habituated to a 180° drawbridge-like motion. The decline and plateau of looking times during habituation are depicted in the left panels of (B). In the Experimental Condition, infants completed two types of test trials, both of which contained a new object on the far side of the display (depicted by the black box). The Impossible Test involved the same full 180° rotation from habituation, but now the screen surprisingly passed through the box as it completed its rotation (with the box disappearing as it became obscured). The Possible Test involved a novel shorter rotation of screen up to the point where it would contact the box, where it stopped; this motion was “possible” in terms of solidity and object permanence, but was more perceptually novel than the Impossible Test. In the Control Condition, the screen rotations were identical, but no new object was presented (such that both motions were equally possible). Within each condition, the two types of test trials were alternated, with order counterbalanced across infants. The results from the test phase are depicted in the right panels of (B). In the Experimental Condition, infants dishabituated to the Impossible Test but not the Possible Test. However, in the Control Condition no preference was observed. These results were interpreted as reflecting the violation of infants' expectations regarding solidity and/or object permanence.

Figure 2

An example of habituation in functional neuroimaging (adapted from Kourtzi and Kanwisher, 2001). (A) In each trial, two stimuli were presented sequentially (each for 300 ms with a 400 ms pause in between). The stimuli were simple shapes presented behind or in front of three partially occluding bars. In the Repeated trials, the same shape was repeated at the same depth with respect to the occluders. In the Novel Contour trials, the same shape was repeated, but moved in depth with respect to the occluders, such that the local visible contours changed. In the Novel Contour + Shape trials, a different shape was presented as the second stimulus, also moved in depth with respect to the occluders. (B) Event-related fMRI responses to the pairs of stimuli in a region of ventral visual cortex that responds more strongly to objects than to other stimulus patterns (lateral occipital complex; LOC). The response to the Novel Contour trials was the same as the response to the Repeated trials, demonstrating that the LOC does not represent visible local contours per se. However, the responses to both of these conditions were attenuated relative to the response to the Novel Contour + Shape condition. These results suggest that the LOC represents perceived shape rather than local contours.