g., upward-green, downward-red. This classical associative conditioning continued 1 hr/day for 20 days and was followed by the third (“posttrain”)

phase of the experiment, in which direction discrimination performance was reassessed using dot patterns of the two colors employed in phase two (red and green). Schlack et al. (2008, Soc. Neurosci., Galunisertib abstract) argued that the associative training of phase two would result in cue-dependent recall-related activity in area MT. Reports of perceived direction of motion in phase three should thus reflect a combination of top-down (imaginal) and bottom-up (stimulus) motion signals. Furthermore, the influence of the imaginal component should depend inversely upon the strength of the stimulus component.

This is precisely what was observed: the psychometric functions for direction discrimination obtained for red and for green moving dot patterns were displaced relative to one another in a manner consistent with perceptual biases introduced by the associated color cue. These psychophysical findings, in conjunction with the previous discovery of recall-related activity in area MT (Schlack and Albright, 2007), lead to the strong prediction that functions for neuronal discriminability (neurometric functions) Palbociclib of motion direction will exhibit biases that mirror the psychophysical bias, reflect cued associative recall, and are accountable by the simple model outlined in Figure 6. Considerations of the balance between stimulus and imagery naturally raise the larger question of whether (and how) an through observer can distinguish between the two if they are both manifested as activation of visual cortex. And, if so, under what conditions does it make a difference? These questions are not new, of course, having been raised repeatedly since the 19th century in discussions of the clinical phenomenon of hallucination (e.g., James, 1890, Richardson, 1969 and Sully, 1888). The studies reviewed herein allow these questions to be addressed in a modern neurobiological context. Most modern neurobiological approaches to these questions skirt the “perceptual equivalence” problem and begin

instead with the premise that the perceptual states elicited independently by stimulus versus explicit imagery are, in fact, quite distinct. While visual cortex may provide a common substrate for representation, the perceptual distinction implies that there are different neuronal states associated with stimulus versus imagery. Human neuropsychological (see Behrmann, 2000, and Bartolomeo, 2002, for review) and fMRI studies (e.g., Lee et al., 2012) support this view. Broadly speaking, lesions of more anterior regions along the ventral visual cortical stream—particularly visual areas of the temporal lobe—may impair the capacity to generate explicit visual images while leaving intact the ability to perceive retinal stimuli (Farah et al.