Contact and posture in nonvisual judgment of gap crossability

The roles of contact and postural components of haptic probing were investigated in 4 experiments. Judgments of the crossability of gaps by blindfolded participants were unimpaired by preventing contact with the far side of the gap and they were not impaired when participants wielded only a flashlight that triggered arbitrary sounds when the light struck either side of the gap. Performance was impaired when perceivers could reach surfaces at varying distances with identical arm movements and, in the 4th experiment, when weights were added to a crossbar of the probe, perceived crossable gap sizes changed in accord with the prediction that the manipulation would alter the perceived posture. These results support a model of nonvisual gap crossing in which different perceptual modalities can provide information that contact has been made but postural information is necessary for perception of the location of that contact.