Visual Scene Processing in Familiar and Unfamiliar Environments

Abstract

Epstein RA, Higgins JS, Jablonski K, Feiler AM. Visual scene processing in familiar and unfamiliar environments. J Neurophysiol 97: 3670 -3683, 2007. First published March 21, 2007 doi:10.1152/jn.00003.2007. Humans and animals use information obtained from the local visual scene to orient themselves in the wider world. Although neural systems involved in scene perception have been identified, the extent to which processing in these systems is affected by previous experience is unclear. We addressed this issue by scanning subjects with functional magnetic resonance imaging (fMRI) while they viewed photographs of familiar and unfamiliar locations. Scene-selective regions in parahippocampal cortex (the parahippocampal place area, or PPA), retrosplenial cortex (RSC), and the transverse occipital sulcus (TOS) responded more strongly to images of familiar locations than to images of unfamiliar locations with the strongest effects (Ͼ50% increase) in RSC. Examination of fMRI repetition suppression (RS) effects indicated that images of familiar and unfamiliar locations were processed with the same degree of viewpoint specificity; however, increased viewpoint invariance was observed as individual scenes became more familiar over the course of a scan session. Surprisingly, these within-scan-session viewpointinvariant RS effects were only observed when scenes were repeated across different trials but not when scenes were repeated within a trial, suggesting that within-and between-trial RS effects may index different aspects of visual scene processing. The sensitivity to environmental familiarity observed in the PPA, RSC, and TOS supports earlier claims that these regions mediate the extraction of navigationally relevant spatial information from visual scenes. As locations become familiar, the neural representations of these locations become enriched, but the viewpoint invariance of these representations does not change.

Two Kinds of fMRI Repetition Suppression? Evidence for Dissociable Neural Mechanisms

“…In contrast, long-interval RS showed a greater degree of viewpoint independence, in that strong RS was observed when previously seen locations were presented again from previously unseen views. As noted in the INTRODUCTION, we observed a similar pattern of results (i.e., greater viewpoint independence for long-interval RS) in earlier experiments (Epstein et al 2005(Epstein et al , 2007a. However, these early experiments measured long-and short-interval RS in different runs during which subjects performed different tasks, so it was possible that the results could be explained by task differences rather than differences in repetition interval.…”

“…These stimuli were used to examine fMRI-RS effects. In previous experiments, we found that fMRI-RS effects in the PPA were unaffected by campus familiarity (Epstein et al 2007a), so we felt confident that results obtained using these images would generalize to images of unfamiliar locations. In addition to the Penn stimuli, 144 images of the Temple University campus (3 views each of 48 different locations) were used as foil stimuli.…”

“…Functional ROIs were defined for each subject using data from the functional localizer scans by identifying sets of contiguous voxels that responded more strongly to scenes than to common objects in the posterior parahippocampal/collateral sulcus region (PPA), retrosplenial/parietal-occipital sulcus region (RSC), and transverse occipital sulcus (TOS). The significance threshold defining these regions was set on a subject-by-subject basis so that ROIs were consistent with those identified in previous studies (Epstein and Kanwisher 1998;Epstein et al 1999Epstein et al , 2007a; thresholds ranged from t Ͼ 2.0 to t Ͼ 4.5. The time course of MR response during the test phase was then extracted from each ROI (averaging over all voxels) and entered into a general linear model in which the nine trial types (new place/no change, new place/view change, new place/place change, new view/no change, new view/view change, new view/place change, old view/no change, old view/view change, old view/place change), along with the foil trials, were represented as impulse response functions convolved with a canonical hemodynamic response function.…”

“…Each run was 8 min 24 s long and was divided into 72 6-s experimental trials during which image pairs were shown, 12 3-s null trials in which a fixation cross was presented on the screen (thus jittering the interval between experimental trials), and 18-s fixation periods at the beginning and end of the scan. Experimental trials began with a 500-ms blank screen, followed by a 700-ms gray screen with a black outline which alerted subjects to the start of a new trial pairing, followed by another 500-ms blank screen, followed by the sequential presentation of two color images for 700 ms each with a 500-ms interstimulus interval (see Epstein et al 2007a for details). A fixation cross was then presented for 2400 ms to complete the trial.…”

“…These studies demonstrated that short-interval RS effects were entirely viewpoint specific, whereas long-interval RS effects showed some degree of viewpoint invariance (Epstein et al 2003(Epstein et al , 2005(Epstein et al , 2007a. It is possible that these results can be explained simply by the fact that short-and long-interval RS were measured in different experimental runs during which subjects performed different behavioral tasks (cf.…”