ИСТИНА

Feature binding is believed to be critical for perception, while brain mechanisms of this process are still under debate. Studies measuring mismatch negativity (MMN) demonstrate that binding occurs at a low level of the cortical hierarchy, while behavioral experiments suggest a much higher integrative level. The current study aimed at testing the hypothesis that processing of feature conjunctions is distributed and may involve two different levels. Experiment 1 combined recording both MMN and behavioral measures. Two types of deviant target stimuli were used – complex stimuli, which required feature conjunctions to be identified, and simple stimuli, which could be identified by a single feature. Responses to complex stimuli were slower and less accurate than responses to simple stimuli. For simple stimuli, errors were associated with increased response time, while there was no such effect for complex stimuli. Errors in response only to complex stimuli – but not to simple stimuli – were associated with decreased MMN amplitude. P300 amplitude was greater for complex stimuli than for simple stimuli. For simple stimuli, P300 amplitude was reduced on erroneous trials. Thus, we replicated within a single experiment the major effects reported in two opposing lines of binding research. Our MMN data hint that the neuronal population encoding feature conjunction is closely associated with (or coincides with) the neuronal population that generates MMN. Our P300 data and behavioral data are compatible with the explanation that higher processing levels receive sensory representations of conjoined features as well as of separate features. Our findings provide resolution to conflicting views concerning the nature of feature binding and support the notion that feature binding is a distributed multi-level process involving bottom-up and top-down interactions. Experiments 2 and 3 involved attentional manipulation – with target stimuli in the auditory and visual modality respectively. Feature conjunction involved tone pitch and location for auditory modality, and Gabor grating orientation and spatial frequency for visual modality. The basic finding from these two experiment was that that MMN was evident only in conditions of voluntary attention directed to a particular feature conjunction. MMN was reduced or abolished in response to ignored nontarget feature conjunctions, as well as in conditions of non-focused attention and cross-modal distraction of attention. Thus, contrary to previous studies of MMN under feature conjunctions, we found that early preattentive feature conjunctions happen on condition of a corresponding top-down attentional control.