Perceptual training of audiovisual simultaneity judgments generalizes across spatial locations

Abstract

Multisensory processing critically depends on the perceived timing of stimuli in the different sensory modalities. Crossmodal stimuli that fall within rather than outside an individual temporal binding window (TBW) are more likely to be bound into a multisensory percept. A number of studies have shown that a short perceptual training in which participants receive feedback on their responses in an audiovisual simultaneity judgment (SJ) task can substantially decrease the size of the TBW and hence increase crossmodal temporal acuity. Here we tested whether multisensory perceptual learning in the SJ task is specific for the spatial locations at which the audiovisual stimuli are presented during training. Participants received feedback about the correctness of their SJ responses for audiovisual stimuli which were presented in one hemifield only. The TBW was assessed separately for audiovisual stimuli in each hemifield before and one day after the training. In line with previous findings, the size of the TBW was significantly reduced after the training phase. Importantly, an equally strong reduction of TBW size was observed in both the trained and the untrained hemifield. Thus, multisensory temporal learning completely generalized to the untrained hemifield, suggesting that the improvement in crossmodal temporal acuity was mediated by higher, location-invariant processing stages. These findings have implications for the design of multisensory training protocols in applied settings such as clinical interventions by showing that training at multiple spatial locations might not be necessary to achieve robust improvements in crossmodal temporal acuity.

Keywords: audiovisual; multisensory processing; perceptual learning; simultaneity judgment; spatial specificity; temporal binding window.

Figure 1.

Estimation of individual TBW size. Triangles show the proportion of correct responses at each SOA for a single participant. Data are shown separately for the pretest (upward triangles) and posttest (downward triangles) in the untrained (left panel) and trained (right panel) hemifield. For each condition, accuracy values were fitted by two logistic regressions, one for negative (auditory leading) and one for positive (visual leading) SOAs. TBW size was derived from the fitted psychometric curves at half the difference between an individual's lowest accuracy point in the baseline session (here 0.5, lower dotted line) and perfect performance (1.0, upper dotted line), indicated by the dashed horizontal line (here at 0.75). The total TBW size for this participant decreased from pretest to posttest by 100 ms in the untrained hemifield and by 103 ms in the trained hemifield (see dashed vertical lines).

Figure 2.

Group mean accuracy at each stimulus onset asynchrony (SOA) in the untrained and trained hemifield. The mean proportion of correct responses is shown separately for the pretest (upward triangles) and the posttest (downward triangles). Negative SOA values indicate auditory leading and positive SOA values indicate visual leading trials. Error bars indicate the SEM.

Figure 3.

Changes in accuracy from pretest to posttest for each participant. The difference in the proportion of correct responses (posttest minus pretest) is shown separately for the untrained and the trained hemifield. Positive values indicate performance increases and negative values indicate performance decreases. Superimposed squares indicate the group mean values (with SEM). The left panel shows changes in accuracy across all stimulus onset asynchrony (SOA) values. Additionally, accuracy changes were calculated separately for the left side (middle panel) of the SOA distribution (i.e., negative or auditory leading SOAs) and the right side (right panel) of the SOA distribution (i.e., positive or visual leading SOAs).

Figure 4.

Changes in TBW size from pretest to posttest for each participant. The difference in the TBW size (pretest minus posttest) is shown separately for the untrained and the trained hemifield. Positive values indicate TBW size decreases and negative values indicate TBW size increases. Superimposed squares indicate the group mean values (with SEM). The left panel shows TBW changes for the total window size (left plus right window size). Additionally, TBW changes were calculated separately for the left window (middle panel) covering the negative (auditory leading) SOAs and the right window (right panel) covering the positive (visual leading) SOAs.