Human posterior parietal cortex responds to visual stimuli as early as peristriate occipital cortex

Abstract

Much of what is known about the timing of visual processing in the brain is inferred from intracranial studies in monkeys, with human data limited to mainly non-invasive methods with lower spatial resolution. Here, we estimated visual onset latencies from electrocorticographic (ECoG) recordings in a patient who was implanted with 112 sub-dural electrodes, distributed across the posterior cortex of the right hemisphere, for pre-surgical evaluation of intractable epilepsy. Functional MRI prior to surgery was used to determine boundaries of visual areas. The patient was presented with images of objects from several categories. Event Related Potentials (ERPs) were calculated across all categories excluding targets, and statistically reliable onset latencies were determined using a bootstrapping procedure over the single trial baseline activity in individual electrodes. The distribution of onset latencies broadly reflected the known hierarchy of visual areas, with the earliest cortical responses in primary visual cortex, and higher areas showing later responses. A clear exception to this pattern was robust, statistically reliable and spatially localized, very early responses on the bank of the posterior intra-parietal sulcus (IPS). The response in the IPS started nearly simultaneously with responses detected in peristriate visual areas, around 60 milliseconds post-stimulus onset. Our results support the notion of early visual processing in the posterior parietal lobe, not respecting traditional hierarchies, and give direct evidence for onset times of visual responses across the human cortex.

The dorsal visual pathway represents object-centered spatial relations for object recognition

“…We documented functional connectivity between IPS and LOC, and show that right pIPS mediates the representation of part relations in ventral regions, and not the other way around. This finding is compatible with research showing that visual object information reaches posterior parietal cortex earlier than ventral regions (Regev et al, 2018), that topological object properties may only become represented in the ventral pathway through feedback connections (Bar et al, 2006;Wang et al, 2020), and that temporary inactivation of posterior parietal regions impairs ventral object processing (Van Dromme et al, 2016;Zachariou et al, 2017). Altogether, these studies suggest a causal role for dorsal cortex in ventral object processing.…”

Intracranial Recordings Demonstrate Both Cortical and Medial Temporal Lobe Engagement in Visual Search in Humans

“…First, a set of findings from noninvasive EEG in humans, and electrophysiology in primates, suggest that pop-out is implemented in parietal cortex (Li et al, 2010;Buschman & Miller, 2007; but see Nobre, Coull, Walsh, & Frith, 2003). This is consistent with reported salience maps in lateral intraparietal cortex (area LIP) in monkeys (Gottlieb, Kusunoki, & Goldberg, 1998) and a broader role for parietal cortex in detecting external visual stimuli, holding such information in memory, and generating motor action plans (Martin et al, 2019;Regev, Winawer, Gerber, Knight, & Deouell, 2018;Xu, 2018;Mangano et al, 2015). By contrast, pFC, including the FEF and lateral frontal cortex, are implicated in search (Li et al, 2010;Buschman & Miller, 2007;Rossi, Bichot, Desimone, & Ungerleider, 2007;Leonards, Sunaert, Van Hecke, & Orban, 2000).…”

Intracranial recordings demonstrate medial temporal lobe engagement in visual search in humans

“…First, a set of findings from non-invasive EEG in humans, and electrophysiology in primates, suggest that Pop-out is implemented in parietal cortex (Li et al, 2010 ;Buschman & Miller, 2007, but see Nobre et al, 2002). This is consistent with reported salience maps in lateral intraparietal cortex (area LIP) in monkeys (Gottlieb et al, 1998); and a broader role for parietal cortex in detecting external visual stimuli, holding such information in memory, and generating motor action plans (Mangano et al, 2015;Xu, 2018;Regev et al, 2018;Martin et al, 2019). By contrast, prefrontal cortex (PFC), including the frontal eye fields (FEF) and lateral frontal cortex are implicated in Search (Leonards et al, 2000;Buschman & Miller, 2007;Rossi et al, 2007;Li et al, 2010).…”