Is attention based on spatial contextual memory preferentially guided by low spatial frequency signals?

Abstract

A popular model of visual perception states that coarse information (carried by low spatial frequencies) along the dorsal stream is rapidly transmitted to prefrontal and medial temporal areas, activating contextual information from memory, which can in turn constrain detailed input carried by high spatial frequencies arriving at a slower rate along the ventral visual stream, thus facilitating the processing of ambiguous visual stimuli. We were interested in testing whether this model contributes to memory-guided orienting of attention. In particular, we asked whether global, low-spatial frequency (LSF) inputs play a dominant role in triggering contextual memories in order to facilitate the processing of the upcoming target stimulus. We explored this question over four experiments. The first experiment replicated the LSF advantage reported in perceptual discrimination tasks by showing that participants were faster and more accurate at matching a low spatial frequency version of a scene, compared to a high spatial frequency version, to its original counterpart in a forced-choice task. The subsequent three experiments tested the relative contributions of low versus high spatial frequencies during memory-guided covert spatial attention orienting tasks. Replicating the effects of memory-guided attention, pre-exposure to scenes associated with specific spatial memories for target locations (memory cues) led to higher perceptual discrimination and faster response times to identify targets embedded in the scenes. However, either high or low spatial frequency cues were equally effective; LSF signals did not selectively or preferentially contribute to the memory-driven attention benefits to performance. Our results challenge a generalized model that LSFs activate contextual memories, which in turn bias attention and facilitate perception.

Figure 1. Experiment 1 task design and results.

a) Trial sequence in the perceptual choice task. A jittered pre-trial fixation was followed by one of two types of image: low or high spatial- frequency filtered sample scene. This was followed by an ISI of 2 refresh rates, and finally the probe images, which were never filtered. Participants had to indicate with a mouse press which of the two images matched the preceding filtered sample (left mouse button for left-sided match, right mouse button for right-sided match). b) Results showed RT and accuracy benefits for probes preceded by LSF filtered sample scenes (error bars represent standard errors).

Figure 2. Paradigm and Results of Experiment 2.

a) Trial sequence in the orienting task. A jittered pre-trial fixation was followed by one of three types of cue: non-filtered, low- or high-spatial-frequency filtered image. This was followed by a variable inter-stimulus interval, and finally the target image, which was never filtered. Participants had to indicate with a mouse press whether or not there was a target currently present in the target image. b) Sensitivity scores and c) reaction times (for target present trials only) for each cue type (NSF, LSF, HSF) by memory condition (memory, no-memory). Error bars represent standard errors.

Figure 3. Results of Experiment 3.

a) Sensitivity scores and b) reaction times (for target present trials only) for each cue type (LSF, HSF) by memory condition (memory, no-memory), grouped by ISI (100 ms, 700 ms). Error bars represent standard errors.