Horizontal target size perturbations during grasping movements are described by subsequent size perception and saccade amplitude

Abstract

Perception and action are essential in our day-to-day interactions with the environment. Despite the dual-stream theory of action and perception, it is now accepted that action and perception processes interact with each other. However, little is known about the impact of unpredicted changes of target size during grasping actions on perception. We assessed whether size perception and saccade amplitude were affected before and after grasping a target that changed its horizontal size during the action execution under the presence or absence of tactile feedback. We have tested twenty-one participants in 4 blocks of 30 trials. Blocks were divided into two experimental tactile feedback paradigms: tactile and non-tactile. Trials consisted of 3 sequential phases: pre-grasping size perception, grasping, and post-grasping size perception. During pre- and post-phases, participants executed a saccade towards a horizontal bar and performed a manual size estimation of the bar size. During grasping phase, participants were asked to execute a saccade towards the bar and to make a grasping action towards the screen. While grasping, 3 horizontal size perturbation conditions were applied: non-perturbation, shortening, and lengthening. 30% of the trials presented perturbation, meaning a symmetrically shortened or lengthened by 33% of the original size. Participants’ hand and eye positions were assessed by a motion capture system and a mobile eye-tracker, respectively. After grasping, in both tactile and non-tactile feedback paradigms, size estimation was significantly reduced in lengthening (p = 0.002) and non-perturbation (p<0.001), whereas shortening did not induce significant adjustments (p = 0.86). After grasping, saccade amplitude became significantly longer in shortening (p<0.001) and significantly shorter in lengthening (p<0.001). Non-perturbation condition did not display adjustments (p = 0.95). Tactile feedback did not generate changes in the collected perceptual responses, but horizontal size perturbations did so, suggesting that all relevant target information used in the movement can be extracted from the post-action target perception.

Biases in the spectral amplitude distribution of a natural scene modulate horizontal size perception

“…Custom MATLAB algorithms (The MathWorks, Massachusetts, United States) were created to compute three-dimensional marker velocities and subsequently calculate the distance between index and thumb markers (known as manual estimate aperture, see Figure 1C ). As in our previous work ( Sanz Diez et al, 2022 ), to estimate participants’ horizontal size perception, manual estimate aperture values were solely considered in those time periods where index and thumb marker velocities were below 5 mm/s. Within those intervals, the manual estimate aperture was identified as the maximum index-thumb distance.…”

The influence of action on perception spans different effectors

“…Although the perceptual phase before and after grasping execution applied to the same target that, in these two moments of the task, was identical in size, they found that, after the grasping action, reports regarding perceptual size showed significant differences that depended on the type of size change that occurred during movement execution. In fact, as shown in Figure 7 , observers reported a smaller size perception when the visual target was lengthened during the grasping execution and no perception modification when the visual target was shortened during the grasping execution (Sanz Diez et al, 2022 ). In both of the studies described above, the perceptual modification occurred according to the type of movement (i.e., reaching or grasping) and to the unpredictable changes of target size during the movement itself, suggesting that this modification can be considered to be a descriptive parameter of the previous motor action (Bosco et al, 2017 ; Sanz Diez et al, 2022 ).…”

“…In fact, as shown in Figure 7 , observers reported a smaller size perception when the visual target was lengthened during the grasping execution and no perception modification when the visual target was shortened during the grasping execution (Sanz Diez et al, 2022 ). In both of the studies described above, the perceptual modification occurred according to the type of movement (i.e., reaching or grasping) and to the unpredictable changes of target size during the movement itself, suggesting that this modification can be considered to be a descriptive parameter of the previous motor action (Bosco et al, 2017 ; Sanz Diez et al, 2022 ).…”

“…These results were consistent in both manual and verbal reports, as is shown in Figure 6 (Bosco et al, 2017 ). Sanz Diez et al ( 2022 ) evaluated size perception after a grasping movement performed toward a visual target that changed in size during the execution of the movement. Although the perceptual phase before and after grasping execution applied to the same target that, in these two moments of the task, was identical in size, they found that, after the grasping action, reports regarding perceptual size showed significant differences that depended on the type of size change that occurred during movement execution.…”

“…(B) Mean Deviation values of grip aperture from the baseline averaged across size perturbation condition. Details as in Figure 5 (modified from Sanz Diez et al, 2022 ). * p < 0.05, significance level.…”