Abstract
Scene-like interactions of pairs of objects (a bird perched on a birdhouse) elicit greater BOLD activity in LOC than the same objects depicted side-by-side (a bird next to a birdhouse) (Kim & Biederman, 2009). Novelty of the interactions (a bird perched on an ear) magnified this gain, an effect that was absent in the side-by-side depictions. LOC is the first cortical stage where shape is distinguished from texture (Cant & Goodale, 2009). Other cortical areas, such as IPS,DLFPC, and PPA did not consistently reveal the pattern of BOLD effects seen in LOC, although it is possible that the effects witnessed in LOC reflected feedback from these areas. Due to the low temporal resolution of the BOLD signal, the time course of these possible effects could not be assessed with fMRI. We used EEG source estimation to determine if interacting and novel depictions produced effects in parietal and prefrontal areas prior to when these effects occurred in occipito-temporal cortex. (The time course of PPA could not be observed with EEG due to its medial location.) While maintaining fixation, subjects performed a one-back task while they viewed a series of two-object displays, presented either as interacting or side-by-side, and in novel or familiar combinations. Occipito-temporal cortex showed earlier divergence of interacting versus side-by-side conditions than parietal cortex. Although novel interactions did not produce a larger BOLD response in parietal cortex, there was a divergence of novelty and familiarity in the EEG signal at about the same time as in occipito-temporal cortex. No consistent pattern was observed in prefrontal cortex. The picture that emerges is one in which scene-like relations are not inferred at some stage following object identification, but are likely achieved simultaneously with the perception of object shape.
NSF BCS 04-20794, 05-31177, 06-17699 to I.B.