A key question in understanding visual awareness is whether any single cortical area is indispensable. In a transcranial magnetic stimulation experiment, we show that observers' awareness of activity in extrastriate area VS depends on the amount of activity in striate cortex (Vl). From the timing and pattern of effects, we infer that back-projections from extrastriate cortex influence information content in Vl, but it is Vl that determines whether that information reaches awareness.
Visual feature binding has been suggested to depend on reentrant processing. We addressed the relationship between binding, reentry, and visual awareness by asking the participants to discriminate the color and orientation of a colored bar and to report their phenomenal awareness of the target features. The success of reentry was manipulated with object substitution masking and backward masking. The results showed that late reentrant processes are necessary for successful binding but not for phenomenal awareness of the bound features. Binding errors (...) were accompanied by phenomenal awareness of the misbound feature conjunctions, demonstrating that they were experienced as real properties of the stimuli . Our results suggest that early preattentive binding and local recurrent processing enable features to reach phenomenal awareness, while later attention-related reentrant iterations modulate the way in which the features are bound and experienced in awareness. (shrink)
We studied the patient JP who has exceptional abilities to draw complex geometrical images by hand and a form of acquired synesthesia for mathematical formulas and objects, which he perceives as geometrical ﬁgures. JP sees all smooth curvatures as discrete lines, similarly regardless of scale. We carried out two preliminary investigations to establish the perceptual nature of synesthetic experience and to investigate the neural basis of this phenomenon. In a functional magnetic resonance imaging (fMRI) study, image-inducing formulas produced larger fMRI (...) responses than non-image inducing formulas in the left temporal, parietal and frontal lobes. Thus our main ﬁnding is that the activation associated with his experience of complex geometrical images emerging from mathematical formulas is restricted to the left hemisphere. (shrink)