The persistence of remote visual semantic memory following ocular blindness.

Subjects with complete ocular blindness in both eyes provide a unique opportunity to study the long-term durability of visual semantic memory. In this cross-sectional study we recruited eleven subjects who had acquired blindness for between 1 and 36 years. For comparison, we studied four subjects with congenital blindness and seventeen age- and sex-matched sighted control subjects. We administered ten forced-choice questionnaires that probed one auditory category and four visual categories, namely object shape and size; object hue and lightness; word and letter shape; and the shape and features of famous faces. Subjects with congenital blindness performed worse than controls on all visual categories, but nevertheless performed better than chance on object structure or colour, suggesting that the answers to some questions about visual properties can be derived from haptic or non-visual semantic information. Subjects with acquired blindness performed similarly to controls on all categories except for facial memory, particularly for facial features. We conclude that there is a substantial "permastore" of visual semantic memory but that facial memories are less durable, perhaps indicating that they are either less over-learned or more dependent on visual representations than other forms of visual object information.