Neural Representation of Targets and Distractors during Object Individuation and Identification

Abstract

In many everyday activities, we need to attend and encode multiple target objects among distractor objects. For example, when driving a car on a busy street, we need to simultaneously attend objects such as traffic signs, pedestrians, and other cars, while ignoring colorful and flashing objects in display windows. To explain how multiple visual objects are selected and encoded in visual short-term memory (VSTM) and in perception in general, the neural object file theory argues that whereas object selection and individuation is supported by inferior intra-parietal sulcus (IPS), the encoding of detailed object features that enables object identification is mediated by superior IPS and higher visual areas such as the lateral occipital complex (LOC). Nevertheless, because task-irrelevant distractor objects were never present in previous studies, it is unclear how distractor objects would impact neural responses related to target object individuation and identification. To address this question, in two fMRI experiments, we asked participants to encode target object shapes among distractor object shapes, with targets and distractors shown in different spatial locations and in different colors. We found that distractor-related neural processing only occurred at low, but not at high, target encoding load and impacted both target individuation in inferior IPS and target identification in superior IPS and LOC. However, such distractor-related neural processing was short-lived as it was only present during the VSTM encoding but not the delay period. Moreover, with spatial cuing of target locations in advance, distractor processing was attenuated during target encoding in superior IPS. These results are consistent with the load-theory of visual information processing. They also show that while inferior IPS and LOC were automatically engaged in distractor processing under low task load, with the help of precuing, superior IPS was able to only encode the task-relevant visual information.

Goal-Directed Visual Processing Differentially Impacts Human Ventral and Dorsal Visual Representations

“…This is consistent with monkey neurophysiology studies showing the prominent role of saliency in driving parietal responses (e.g., Gottlieb et al, 1998; see also Constantinidis and Steinmetz, 2005;Bisley and Goldberg, 2006). Nevertheless, the present study showed that dorsal regions exhibited a stronger filtering of the task-irrelevant information than ventral regions, consistent with prior findings using fMRI response amplitude measures (e.g., Xu, 2010;Jeong and Xu, 2013).…”

“…The existence of top-down attentional control signals in parietal cortex (Corbetta and Shulman, 2002; Yantis and Serences, 2003) and task modulation of parietal visual responses (e.g., Toth and Assad, 2002;Todd and Marois, 2004;Freedman and Assad, 2006;Xu and Chun, 2006;Gottlieb and Synder, 2010;Xu, 2010;Liu et al, 2011;Jeong and Xu 2013;Xu and Jeong, 2015;Shomstein and Gottlieb, 2016;Bracci et al, 2017) suggest that task may exert a stronger impact on visual representations in the dorsal than ventral pathway. However, some studies have failed to find such an effect (Konen and Kastner, 2008;Harel et al, 2014).…”

Individuation of objects and object parts rely on the same neuronal mechanism

“…These areas are known to be tuned to object quantities in humans434445 as well as in other animal species4647. Our data, showing that individuation of object parts is reflected by the N2pc component, extend this view by suggesting that within-object quantity is also efficiently coded by these areas.…”

The neural basis of temporal individuation and its capacity limits in the human brain

“…This process is crucial for registering individual items as distinct perceptual events and is thought to underlie observers' impaired ability to discriminate between separate occurrences of objects with the same identity relative to those with different identities (Kanwisher 1987). Although observers show capacity limits associated with individuating items across both time and space (e.g., Kanwisher 1991;Kanwisher and Potter 1989;Caramazza 1995, 1996), and previous studies have begun to identify the neural correlates of spatial individuation (e.g., Jeong and Xu 2013;Xu 2009;Xu andChun 2006, 2007), no study has identified the neural substrates underlying temporal individuation. In the present study we used functional magnetic resonance imaging (fMRI) to investigate the brain regions and mechanisms that are involved in the successful individuation of temporally distinct objects during encoding and how disruptions to this process are represented in the brain.…”