Enhanced Tactile Memory in the Blind

In the blind, areas of the brain that would normally respond to visual stimuli instead of process information from other sensory modalities such as the somatosensory and auditory domains. Recent studies have shown that the visual cortex of the blind participates in higher-order processing of auditory information including verb generation and retrieval of verbal memories. Because tactile information plays a similarly crucial role when vision is missing (i.e. to read Braille), it has been suggested that the ability to encode and recall tactile information in the blind is superior to that in the sighted.

OBJECTIVES:

The first objective of this protocol is to determine if tactile memory is superior in early blind subjects relative to that in late blind and sighted control subjects.

The second objective is to determine if the visual cortex of blind people can participate in higher-order processing of tactile information such as tactile encoding recognition.

STUDY POPULATION:

Our experiments will make use of early blind, late blind, and sighted control subjects.

DESIGN:

Experiment 1: We will quantify the ability of our study populations to encode into and retrieve from episodic tactile memory. Subjects will be presented with a series of surfaces that they are to palpate and commit to memory, after which they will rest for ten to fifteen minutes. The old surfaces will then be presented again with a same number of new surfaces randomly interleaved. Subjects are to discriminate old from new surfaces.

Experiment 2: We will identify cortical areas associated with successful tactile memory encoding and retrieval in blind individuals and sighted controls using functional magnetic resonance imaging (fMRI). Subjects will perform the memory task from Experiment 1 while in the MRI machine.

OUTCOME MEASURES:

Experiment 1: The primary outcome measure will be recognition memory, a corrected measure of the number of old stimuli correctly remembered.

Experiment 2: The primary outcome measure will be the number of voxels significantly activated in primary visual cortex in early blind subjects as compared to late blind subjects and sighted controls.

We expect the magnitude of visual cortex activation in the early blind during a tactile memory task to correlate with superior performance on the task.