ИСТИНА

Feature binding is believed to be critical for perception, while mechanisms of this process remain 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 may involve both levels. EEG was recorded while participants were engaged in an auditory two-alternative choice task, which was a combination of the oddball and condensation tasks. 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. MMN was prominent and its amplitude did not differ between simple and complex stimuli – although the stimuli deviated from standards either in a single feature or in two features correspondingly. Errors in response only to complex 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 are compatible with the explanation that higher processing levels receive sensory representations of conjoined features as well as of separate features. Thus, the increased informational load created by complex stimuli prolongs processing time – leading to increased response time for the stimuli that require feature conjunction to be identified. 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.