Material-specific processes in tactile short-term memory

Abstract

Studies concerning tactile short-term memory (short-term memory or the sense of touch) have often been contradictory. Some of these studies support the existence of modality-specific tactile memory, a separate, independent storage system for tactile information. Other studies do not support such a system. Further, confusion has arisen regarding the tactile test materials, since many of them use common shapes which are easily labeled verbally. It is hypothesized that information which can be labeled is stored in material-specific verbal memory in the left hemisphere, while patterned or spatial information is stored in material-specific nonverbal memory in the right hemisphere. This paper reports two studies conducted to demonstrate both verbal and nonverbal material-specific memory using tactile test materials. The first experiment utilized the Seguin Formboard, which has wooden shapes that are easily labeled verbally. The test was administered to brain damaged patients and to normal controls. Results showed that the performance of the people with left hemisphere brain damage was significantly impaired relative to the normal controls. This was expected since verbal material is processed in the left hemisphere. People with damage in this area have difficulty naming objects and storing the names. The second experiment utilized wooden shapes that were presumed difficult to label. This test was again administered to brain damaged subjects as well us to normal controls. The results were not significant. This may have been because the test was too difficult or because it did not tap nonverbal spatial information. Thus, people with right hemisphere damage were expected to have difficulty processing this type of material. The right damaged group did tend to do more poorly than the other groups. It is not known if this difference would be significant were the test simplified, or if there were actually no group differences. The first study suggests that the Seguin Formboard, thought to be a nonverbal tactile memory test, is actually verbally mediated. The second study did not yield significant results, but suggests a line of further research into the area of nonverbal material-specific memory tested in the tactile modality. These experiments suggest the importance of carefully evaluating test materials to determine what abilities they actually measure in order to obtain a fine analysis of memory function.