Content area
Abstract
Object substitution masking (OSM) refers to a failure of a target to reach conscious awareness when it is surrounded by dots sharing a common onset but remaining visible after target removal. This effect has been hypothesized to reflect reentrant (feedback) visual processes that result in the mask replacing the target representation. This notion of substitution has been implicated in a variety of topics regarding spatiotemporal object perception including the attentional blink (AB), change blindness, and inattentional blindness. Although a number of studies have explored the OSM phenomenon, few of them have examined the depth of processing associated with the masked targets. The present set of experiments use event-related brain potentials (ERPs) to investigate the depth of processing issue in OSM by focusing on components tied to specific processing stages. Experiment 1 examined the effect of OSM on the N400 component, which reflects the degree of semantic mismatch between a target and its context. Delayed offset of the masking dots reduced both the target's detectability as well as its N400 amplitude, showing that OSM reduces or eliminates semantic processing. Experiment 2 evaluated whether OSM also affects processing stages preceding semantic analysis by examining OSM effects on the N170 component of the ERP. The N170 has a latency of approximately 170 ms after stimulus onset and is larger for faces than other objects such as houses. The relatively short latency of the N170 and its insensitivity to the identity of the faces suggests that it reflects the structural encoding of faces at a basic level of categorization. Participants classified images as either faces or houses in the presence of masking dots with either simultaneous or delayed offsets. Similar to Experiment 1, delayed offset of the masking dots significantly reduced the accuracy of the face-house discrimination as well as reducing the amplitude of the N170 component. These findings offer the first neural evidence that substitution interferes with target processing early in visual processing, prior to semantic analysis (with linguistic stimulus) and preceding categorization stages during object recognition. Results are considered within the context of reentrant processing as well as how OSM relates to other phenomena such as the attentional blink.
