Simultaneity and Temporal Order Judgments Are Coded Differently and Change With Age: An Event-Related Potential Study

Abstract

Multisensory integration is required for a number of daily living tasks where the inability to accurately identify simultaneity and temporality of multisensory events results in errors in judgment leading to poor decision-making and dangerous behavior. Previously, our lab discovered that older adults exhibited impaired timing of audiovisual events, particularly when making temporal order judgments (TOJs). Simultaneity judgments (SJs), however, were preserved across the lifespan. Here, we investigate the difference between the TOJ and SJ tasks in younger and older adults to assess neural processing differences between these two tasks and across the lifespan. Event-related potentials (ERPs) were studied to determine between-task and between-age differences. Results revealed task specific differences in perceiving simultaneity and temporal order, suggesting that each task may be subserved via different neural mechanisms. Here, auditory N1 and visual P1 ERP amplitudes confirmed that unisensory processing of audiovisual stimuli did not differ between the two tasks within both younger and older groups, indicating that performance differences between tasks arise either from multisensory integration or higher-level decision-making. Compared to younger adults, older adults showed a sustained higher auditory N1 ERP amplitude response across SOAs, suggestive of broader response properties from an extended temporal binding window. Our work provides compelling evidence that different neural mechanisms subserve the SJ and TOJ tasks and that simultaneity and temporal order perception are coded differently and change with age.

Keywords: aging; audiovisual; event-related potentials; multisensory integration; simultaneity perception; temporal binding window; temporal order perception.

FIGURE 1

SJ task (left) and the TOJ task (right), presented with the SOAs of ±70 and ±270 ms. In both of the tasks, the one stimulus of the audiovisual pair (sound in this example) can appear 1–3 s following the fixation cross and another stimulus (light in this example) appears either ±70 or ±270 ms relative to the other stimulus. The figure depicts the auditory stimulus (i.e., beep) as presented 270 ms before the visual stimulus (i.e., flash). Note, that the design is the same for both of the tasks and only the question asked is different.

FIGURE 2

Simultaneity judgment (SJ): average (thick lines) and individual (thin lines). Gaussian data fits showing that younger adults (black) and older adults (gray) require the visual stimulus to be presented approximately 126 and 147 ms prior to auditory stimulus in order to perceive the two stimuli as simultaneous, respectively.

FIGURE 3

Temporal order judgment (TOJ): average (thick lines) and individual (thin lines). Sigmoidal data fits showing that younger adults (black) and older adults (gray) require the auditory stimulus to be presented approximately 20 and 7 ms prior to visual stimulus in order to perceive the two stimuli as simultaneous, respectively.

FIGURE 4

Average PSS (left) and TBW (right) for the SJ and TOJ tasks. The gray circles represent each individual participant’s data whereas the black circle represents the average obtained from younger adults (A,B) and older adults (C,D). Significant differences in PSS as well as TBW were obtained between the two tasks. ^∗∗p < 0.01. Error bars are ±1 SEM.

FIGURE 5

Average TBW for younger and older adults for the TOJ task. The gray circles represent each individual participant’s data whereas the black circle represents the average obtained from each group. A significant difference between the means of the two groups was not obtained. Error bars are ±1 SEM.

FIGURE 6

Average amplitude (μV) of visual P1 ERPs from the within-subjects analysis obtained from the control condition from younger (A,B) and older (C,D) adults in response, and time-locked, to the flash stimulus (light bulb icon) from the visual-auditory conditions (sound, speaker icons, presented 70 or 270 ms after light) obtained from the O2 and P4 electrodes for the TOJ and SJ tasks.

FIGURE 7

Average amplitude (μV) of auditory N1 ERPs from the control condition from younger (A) and older (B) adults in response, and time-locked, to the beep stimulus (sound icon) from the auditory-visual conditions (light, light bulb icon, presented 70 or 270 ms after sound) obtained from the FCz electrode for the TOJ and SJ tasks.

FIGURE 8

Average amplitude (μV) of visual P1 ERPs from the between-subjects analysis obtained from the control condition from younger and older adults in response, and time-locked, to the flash stimulus (light bulb icon) from the visual-auditory conditions [sound, speaker icons, presented 70 ms after light (A) and 270 ms after light (B)] obtained from the O2 electrode for the TOJ and SJ tasks.

FIGURE 9

Average amplitude (μV) of auditory N1 ERPs from the experimental condition from younger and older adults time-locked to light in response to the beep stimulus (sound icon) from the visual-auditory conditions [sound, speaker icons, presented 70 ms after light (A) and 270 ms after light (B)] obtained from the FCz electrode for the TOJ and SJ tasks.

FIGURE 10

Average amplitude (μV) of auditory N1 ERPs from the experimental condition from younger and older adults in response, and time-locked, to the beep stimulus (sound icon) from the visual-auditory conditions [sound, speaker icons, presented 70 ms after light (A) and 270 ms after light (B)] obtained from the FCz electrode for the TOJ and SJ tasks.