Essay 13.4 Haptic Memory

Do people remember their touch experiences in the same way that they remember events experienced in other modalities? An important distinction in other modalities is between “implicit” and “explicit” memories. When memory is explicit, one has a feeling of remembering the past. When memory is implicit, one behaves in a way that reflects past experience, but without recollecting that experience. Suppose you usually keep your breakfast cereal in one cupboard, and one day you make a switch. If you now mistakenly go to the cupboard that used to hold the cereal, you are demonstrating implicit memory. This is likely to be followed by your explicitly remembering that you moved the cereal!

In a typical laboratory experiment, an explicit memory test requires people to recall or recognize a set of items they experienced before. An implicit memory test involves measuring a change in response to previously experienced items, but the participants are not asked to remember being exposed to them. Explicit memory and implicit memory have been distinguished experimentally by manipulating how items are studied. Suppose people study items either meaningfully or superficially and then are tested on what they remember about the items. On explicit memory tests, they tend to perform better after meaningful study. But performance on implicit memory tests generally does not depend on how the items were studied. That is, people respond differently to previously studied items regardless of the form of study.

Touch, like other modalities, shows explicit and implicit forms of memory. In a haptic version of this type of experiment (Srinivas et al., 1997), all participants studied a set of two-dimensional patterns by feeling them. In one condition, while feeling a form they generated a useful function that it could serve (for example, it could be a coat hanger), while in another condition they reported the number of lines in the form while feeling it. On an explicit test of memory that involved discriminating previously studied forms from new ones, performance was better after the function-generation task than after the line-counting task. This result shows that meaningful study facilitated explicit memory. But on an implicit test of memory that required subjects to feel a form (previously studied or new) and then to draw it, performance was unaffected by the nature of prior study. They did better at drawing forms they had previously been exposed to, regardless of whether they had counted the lines in the forms or generated a useful function for them. Therefore, it appears that both implicit and explicit haptic memories operate in the same fashion as do memories from other sensory modalities.