Date Published: March 21, 2019
Publisher: Public Library of Science
Author(s): Joëlle Hajj, Dana Maslovat, Erin K. Cressman, Laura St. Germain, Anthony N. Carlsen, Michael B. Steinborn.
Recent research has suggested that visual discrimination and detection may be enhanced during movement preparation and execution, respectively. The current study examined if visual perceptual processing is augmented prior to or during a movement through the use of an Inspection Time (IT) task. The IT task involved briefly presenting (e.g., 15–105 ms) a “pi” figure with differing leg lengths, which was then immediately masked for 400 ms to prevent retinal afterimages. Participants were subsequently required to choose which of the two legs was longer. In Experiment 1, participants (n = 28) completed the IT task under three movement conditions: no-movement (NM), foreperiod (FP), and peak velocity (PV). In the NM condition, participants solely engaged in the IT paradigm. In the FP condition, the IT stimulus was presented prior to movement execution when response planning was expected to occur. Finally, in the PV condition, participants made a rapid movement to a target, and the IT stimulus was presented when their limb reached peak velocity. In Experiment 2, participants (n = 18) also performed the IT task in the PV and NM condition; however, vision of the limb’s motion was made available during the PV trials (PV-FV) to investigate the potential influence of visual feedback on IT performance. Results showed no significant differences in performance in the IT task between the NM and FP conditions, suggesting no enhancement of visual processing occurred due to response preparation (Experiment 1). However, IT performance was significantly poorer in the PV condition in comparison to both the NM and FP conditions (Experiment 1), and was even worse when visual feedback was provided (Experiment 2). Together, these findings suggest that visual perceptual processing is degraded during execution of a fast, goal-directed movement.
In their seminal work, Goodale and Milner  showed that vision for perception is processed differently and via a separate pathway compared to vision for action. In particular, Goodale and Milner’s dual systems model suggests that visual information used to guide movements online is processed by a dorsal visual stream, whereas visual perceptual processing occurs predominantly via a much slower ventral visual stream. Although perceptual processing is the slower of the two modes, some anecdotal accounts have suggested that visual perceptual processing may be upregulated during movement. For example, professional baseball and tennis players have reported experiencing a “slowing-down” of the ball just prior to contact. Recent studies have investigated whether this purported upregulation of visual perception might occur before  and/or during  goal-directed movement. For example, Hagura and colleagues  investigated whether planning for a goal-directed movement alters visuo-temporal discrimination ability. They found that motor preparation not only influenced the perception of the duration of a visual stimulus, but also the perceived rate of flow of visual information, as rapidly presented sequences of letters were more accurately perceived when presented just prior to a reaching movement .
The present study aimed to establish if inspection time is altered by preparation and/or execution of a goal-directed movement. Inspection time has been suggested to provide insight into processing time for visual perception [8, 10]. To test visual processing, a perceptual IT task was completed prior to and during a goal-directed limb movement. We expected that if visual processing is upregulated at peak-limb velocity then presentation of the IT stimulus during the fastest part of the movement would result in improved IT performance in comparison to that observed in the NM condition. Likewise, if visual perceptual processing was enhanced by motor preparation, then performance in the IT paradigm would be better when the IT stimulus was presented during the RT foreperiod of a goal-directed limb movement in comparison to when it was presented while sitting idly (NM condition). These expectations were based on previous literature that found improved visual perceptual ability when visual stimuli were presented during a RT foreperiod  and at peak-limb velocity . Contrary to expectations, however, the first experiment showed that performance on the IT task in the FP condition was not significantly different from performance in the NM condition, providing no evidence for visuo-perceptual enhancement due to motor preparation. In the PV condition, performance on the IT task was significantly poorer in comparison to the NM condition, even though the stimuli were presented at similar times following the acoustic stimulus (Fig 3A). Moreover, the second experiment replicated and confirmed these results, and showed further degradation in IT performance when online visual feedback was provided (Fig 3B).
In summary, no evidence for increased visual perceptual processing at peak velocity of a goal-directed movement was found in the present experiments. In contrast, the speed of visual processing appears to have decreased during movement production, which was further exacerbated by the provision of online visual feedback. The most likely explanation for these results is that during movement production fewer attentional resources were available to perform the IT task concurrently with the movement task. Although no improvement in visual inspection time was found during the foreperiod of a goal-directed movement, these findings may be attributable to the presentation time of the visual stimuli with respect to the go-signal. However, the present results do suggest that the requirement to perform a perceptually demanding task interferes with the preparation of an upcoming movement. Overall, these results indicate that the perceptual processing of visual information is modulated based on perceived task-related priorities during movement execution.