Abstract
Behavioral and electrophysiological evidence suggests that visual attention operates in parallel at distinct spatial locations and samples the environment in periodic episodes. This combination of spatial and temporal characteristics raises the question of whether attention samples locations in a phase-locked or temporally independent manner. If attentional sampling rates were phase locked, attention would be limited by a global sampling rate. However, if attentional sampling rates were temporally independent, they could operate additively to sample higher rates of information. We tested these predictions by requiring participants to identify targets in 2 or 4 rapid serial visual presentation (RSVP) streams, synchronized or asynchronized to manipulate the rate of new information globally (across streams). Identification accuracy exhibited little or no change when the global rate of new information doubled from 7.5 to 15 Hz (Experiment 1) or quadrupled to 30 Hz (Experiment 2). This relatively stable identification accuracy occurred even though participants reliably discriminated 7.5 Hz synchronous displays from displays globally asynchronized at 15 and 30 Hz (Metamer Control Experiment). Identification accuracy in the left visual field also significantly exceeded that in the right visual field. Overall, our results are consistent with temporally independent attention across distinct spatial locations and support previous reports of a right parietal “when” pathway specialized for temporal attention.
Highlights
Behavioral and electrophysiological evidence suggests that visual attention operates in parallel at distinct spatial locations and samples the environment in periodic episodes
As early as 1910, psychologists posited that attention is deployed in episodic intervals (Tichener, 1910). Support for this claim has been intermittent, recent psychophysical studies provide evidence for episodic sampling in visual attention. Much of this evidence comes from experiments that embed two targets in rapid serial visual presentation (RSVP) displays
This finding could reflect temporal independence between neural resources dedicated to the left and right hemifields. This finding could reflect temporal independence across sufficiently distinct spatial locations, regardless of whether those locations occur in different hemifields. To distinguish between these possibilities, in Experiment 2 we presented multistream RSVP sequences similar to those used by Scalf et al (2007)
Summary
Behavioral and electrophysiological evidence suggests that visual attention operates in parallel at distinct spatial locations and samples the environment in periodic episodes. These findings corroborate several behavioral studies, which suggest that attention samples one or more locations at consistent rates of 7 to 10 Hz (Dugué & Vanrullen, 2014; Landau & Fries, 2012; VanRullen et al, 2007) Together, these results support the notion that visual attention is deployed in periodic episodes. The Bblinking spotlight^ model posits that a single attentional resource samples multiple locations in successive temporal intervals (VanRullen et al, 2007; VanRullen & Dubois, 2011) Unlike competing models, this model assumes that attentional resources cannot be divided among multiple locations at once (a Bmultiple spotlights^ account; Bay & Wyble, 2014; McMains & Somers, 2004; Gray et al, 2014; Spaak et al, 2014). These bilateral advantages suggest that parallel resources control attention in the LVF and RVF (Alvarez & Cavanagh, 2005; Chakravarthi & Cavanagh, 2009; Reardon, Kelly, & Matthews, 2009; Alvarez, Gill, & Cavanagh, 2012)
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