Model of predicted SI cortical activity in response to specific conditions of tactile stimulation. This model is an extension of the Vierck and Jones model (1970) on two-point receptive fields. a. When stimuli consisting of two points are oscillated on the skin at low-frequency 25 Hz flutter at distant sites, the peaks of SI response are distinct and non-overlapping, and therefore the subject is easily able to discriminate between the two points. b. As the points are positioned at stimulus sites that are closer together, the peaks begin to overlap. Because the peaks are no longer easily distinguishable, discriminability is reduced. c. Adding a same-site high-frequency 200 Hz vibration to the flutter stimuli ("complex" stimuli) has been shown to reduce the spatial extent of the peaks of response in SI and, as found in the present study, would make it easier to distinguish between two points on the skin. d. Presentation of a stimulus at the same skin site on the unattended hand would reduce the magnitude of SI response by flutter stimulation. This reduction in magnitude of SI response would consequently lead to a reduction in the clarity (or contrast) between the activity evoked by the adjacent, or near-adjacent, cortical regions activated by the two stimuli, and as a result, lead to a decrease in spatial acuity.