The effect of haptic cues on motor and perceptual based implicit sequence learning

Abstract

We introduced haptic cues to the serial reaction time (SRT) sequence learning task alongside the standard visual cues to assess the relative contributions of visual and haptic stimuli to the formation of motor and perceptual memories. We used motorized keys to deliver brief pulse-like displacements to the resting fingers, expecting that the proximity and similarity of these cues to the subsequent response motor actions (finger-activated key-presses) would strengthen the motor memory trace in particular. We adopted the experimental protocol developed by Willingham (1999) to explore whether haptic cues contribute differently than visual cues to the balance of motor and perceptual learning. We found that sequence learning occurs with haptic stimuli as well as with visual stimuli and we found that irrespective of the stimuli (visual or haptic) the SRT task leads to a greater amount of motor learning than perceptual learning.

Keywords: haptic cue; motor memory; sequence learning; serial reaction time task.

FIGURE 1

A schematic diagram of the experimental apparatus and setup. Four lever-shaped keys were motorized using flat voice coil motors (VCMs) and placed under computer control. The keys were spaced 6.5 cm centerline to centerline (dimension a). Visual stimuli were presented by the lighting of four horizontally positioned red LEDs spaced 5 cm apart (dimension b) and haptic stimuli were provided by the injection of an upward half-sinusoid pulse in the reference position of the key. A participant sat and rested her/his ring and index fingers of both hands on the keys. The center of the four LEDs was about 90 cm away from the participant’s eyes (dimension c). She/he was allowed to adjust the height of the chair for comfort and the participant’s view of her/his hands was occluded using a box. White noise was presented through headphones.

FIGURE 2

The command signals for visual and haptic stimuli and recorded responses. (A) The control signal to turn on/off the LED for visual stimuli. (B) The reference position to be followed by the tip of the key for haptic stimuli. (C) A sample of a typical recorded trajectory responding to a visual stimulus. (D) A sample of typical recorded trajectories in response to a haptic stimulus (dashed line: without the finger resting on the key, solid line: with the finger resting on the key). Reaction time (RT) was defined as the difference between the initial stimulus command and the point at which the key crosses the threshold. Both visual and haptic stimuli were presented for a 100 ms time interval.

FIGURE 3

Mean by group and subgroup of individual median RTs for the training phase (blocks 1–10) and transfer phase (blocks 11–14). Error bars are ± 1 standard error of the mean. R and S stand for pseudorandom and sequenced stimuli, respectively.

FIGURE 4

Mean by group and subgroup of individual error rates for the training phase (blocks 1–10) and transfer phase (blocks 11–14). Error bars are ± 1 standard error of the mean. R and S stand for pseudorandom and sequenced stimuli, respectively.

FIGURE 5

Training RT Score and Transfer RT Score. The Training RT Score is defined as a difference in RT between the means of blocks 8 and 10 and block 9, and the Transfer RT score is defined as a difference in RT between the means of blocks 12 and 14 and block 13. (A) Training RT Scores of the visual and haptic groups (no differences in the cues presented to the subgroups in the training phase). (B) Transfer RT Score of the visual-perceptual, haptic-perceptual, visual-motor, and haptic-motor subgroups. (C) Pooled Transfer RT Score (averaged across the visual and haptic groups) in each condition. The motor group shows a significantly greater pooled Transfer RT Score than the perceptual group (ANOVA, p = 0.044). Error bars are ± 1 standard error of the mean. An asterisk on a line linking bars indicates a significant difference between two groups (subgroups) while an asterisk above a bar indicates a significant difference from zero.

FIGURE 6

Training Error Score and Transfer Error Score. The Training Error Score is defined as a difference in error rate between the means of blocks 8 and 10 and block 9, and the Transfer Error score is defined as a difference in error rate between the means of blocks 12 and 14 and block 13. (A) Training Error Scores of the visual and haptic groups. There is a significant difference between the two groups (t-test, p = 0.043). (B) Transfer Error Score of the visual-perceptual, haptic-perceptual, visual-motor, and haptic-motor subgroups. (C) Pooled Transfer Error Score (averaged across the visual and haptic groups) in each condition. Error bars are ± 1 standard error of the mean. An asterisk on a line linking bars indicates a significant difference between two groups (subgroups) while an asterisk above a bar indicates a significant difference from zero.