Altered representation of peripersonal space in the elderly human subject: a sensorimotor approach.

The representation of the peripersonal space in humans and its modification with aging were studied by analyzing three-dimensional arm movements in healthy young and elderly adults. Participants drew ellipses in three reference planes (sagittal, frontal and horizontal), and errors in the orientation of ellipses with regard to the planes were measured. All subjects showed large disparities in the errors in different planes, errors were maximal in the horizontal plane. These findings imply that different planes are centrally represented with different errors and suggest that the mental representation of peripersonal space is anisotropic. Moreover, the elderly made larger errors than young subjects, regardless of the reference plane. Thus, the space representation is altered with aging. Compared with young adults, the elderly underestimate volume in space, a phenomenon that can be called the compression of space representation.