ERP evidence for the influence of scene context on the recognition of ambiguous and unambiguous objects

We are used to seeing objects in specific settings, and in association with other related objects. This contextual information allows for fast and efficient object recognition and influences brain-related processes. The influence of scene context has been studied using event-related potentials (ERPs) in order to further our understanding of the underlying brain mechanisms. Current ERP studies have focused on effects related to the incongruity between unambiguous objects and their scenes, rather than the specific influence of a congruent scene. The present study sought to examine ERPs associated with the beneficial influence of scene context on object recognition. This influence was examined using ambiguous objects that required a congruent scene in order to be recognized, as well as unambiguous objects, to determine whether scene processing occurs even when it is unnecessary for recognizing the object. Twenty healthy subjects were instructed to indicate whether they recognized, had a vague idea, or did not recognize target objects that appeared within congruent and neutral scenes. ERPs from 250 to 1000 ms, including the N300 and N400, were more positive at anterior sites and more negative at posterior sites, when objects appeared in congruent scenes as opposed to when they appeared in neutral scenes, with a larger effect seen for ambiguous objects. Upon further examination, the results showed that the ERPs to ambiguous objects became similar to those of unambiguous objects when they appeared in congruent contexts. These findings indicated that a congruent context exerted its influence by reducing the ambiguity of objects.

Effects of contextual information and stimulus ambiguity on overt visual sampling behavior

The sampling of our visual environment through saccadic eye movements is an essential function of the brain, allowing us to overcome the limits of peripheral vision. Understanding which parts of a scene attract overt visual attention is subject to intense research, and considerable progress has been made in unraveling the underlying cortical mechanisms. In contrast to spatial aspects, however, relatively little is understood about temporal aspects of overt visual sampling. At every fixation, the oculomotor system faces the decision whether to keep exploring different aspects of an object or scene or whether to remain fixated to allow for in-depth cortical processing - a situation that can be understood in terms of an exploration-exploitation dilemma. To improve our understanding of the factors involved in these decisions, we here investigate how the level of visual information, experimentally manipulated by scene context and stimulus ambiguity, changes the sampling behavior preceding the recognition of centrally presented ambiguous and disambiguated objects. Behaviorally, we find that context, although only presented until the first voluntary saccade, biases the perceptual outcome and significantly reduces reaction times. Importantly, we find that increased information about an object significantly alters its visual exploration, as evident through increased fixation durations and reduced saccade amplitudes. These results demonstrate that the initial sampling of an object, preceding its recognition, is subject to change based on the amount of information available in the system: increased evidence for its identity biases the exploration-exploitation strategy towards in-depth analyses.