Influence of imaged pictures and sounds on detection of visual and auditory signals.

The present study compared sensitivity for auditory and visual signals in a simple detection task and in a related task in which ,9 was also imaging mental pictures and sounds. Sensitivity (rf') was reduced during imagery; within the imaging conditions, it was smaller when image and signal were both auditory or both visual than for cross-modal conditions and smaller with unfamiliar than familiar images. Likelihood ratio (Lx) was also smaller in the isomodal imaging conditions, as there were more visual false alarms during visual imagery and more auditory false alarms during auditory imagery. The data are not consistent with the assumption that d' is lower during imagery due to distraction; they do not entirely fit a channel competition model, but suggest that imagery functions as an internal signal which is confused with the external signal. Perky's (1910) effect has been difficult to explain: she found that if Os were asked to describe their images of common objects while dim facsimiles of the objects were presented before them, they reported only an imagery, not a perceptual, experience. This finding seemed paradoxical: in ordinary situations, imagery can be distinguished from real stimuli virtually 100% of the time; yet Perky's Os confused external stimuli with the images they were describing and seemed unable to discriminate the real physical signals. It is possible to explain the seeming inconsistency between Perky's experiment and everyday experience by inferring that the two events are at antipodal points on a continuum. The continuum would represent a class of conscious events characterized by activity in the sensory pathways and some central expectancies and memories, encompassing both