Representations of single and compound stimuli in negative and positive patterning.

In four experiments, rats were trained on different patterning discriminations before being tested with compounds composed of novel combinations of the trained stimuli. In Experiment 1, rats were trained on a negative-patterning schedule (A+ B+ AB-) intermixed with reinforced presentations of a second compound (CD+). On a subsequent test, the rats responded more to two novel compounds, AC and BD, than to A and B, but less than to CD. In Experiment 2, rats were trained on two concurrent negative-patterning discriminations (A+ B+ AB-, C+ D+ CD-). On test, they responded more to AC and BD than to AB and CD, but less than to the single stimuli. In Experiment 3, rats were trained on two concurrent positive-patterning discriminations (A- B- AB+, C- D- CD+). On test, their response rates to AC and BD were not different from the response rates to the trained compounds (AB and CD). Finally, in Experiment 4, rats were trained on a positive- and negative-patterning discrimination concurrently. Once again, on test, response rates to AC and BD were not different from responding on reinforced trials of the trained discriminations (A+, B+, and CD+). We discuss the implications of these findings for elemental and configural models of stimulus representation.

Noninformative vision causes adaptive changes in tactile sensitivity.

The last few years have witnessed a rapid growth of research investigating how information is integrated across sensory modalities, a process at the core of our everyday perceptual experiences. The present study focuses on the integration of vision and touch and, in particular, how tactile perception is affected by a view of the relevant body part containing no information about the tactile stimulus itself. Previous studies have established that this "noninformative vision" can improve subsequent tactile discrimination (Kennett et al., 2001; Taylor-Clarke et al., 2004a), a finding we confirm in the present study. However, we also report here that noninformative vision impairs the detection of tactile stimuli and the discrimination of near-threshold stimuli. These effects are shown to resemble, and indeed combine additively with, shifts in discrimination and detection thresholds produced by adaptation to suprathreshold tactile stimulation. We conclude that noninformative vision of the body does not simply enhance somatosensory processing, but rather it induces adaptive changes in tactile sensitivity via shifts in gain control operating within a bimodal sensory system. This constitutes a novel means by which vision of the body can alter tactile perception.