Age-Related Changes in Temporal Binding Involving Auditory and Vestibular Inputs

Abstract

Maintaining balance involves the combination of sensory signals from the visual, vestibular, proprioceptive, and auditory systems. However, physical and biological constraints ensure that these signals are perceived slightly asynchronously. The brain only recognizes them as simultaneous when they occur within a period of time called the temporal binding window (TBW). Aging can prolong the TBW, leading to temporal uncertainty during multisensory integration. This effect might contribute to imbalance in the elderly but has not been examined with respect to vestibular inputs. Here, we compared the vestibular-related TBW in 13 younger and 12 older subjects undergoing 0.5 Hz sinusoidal rotations about the earth-vertical axis. An alternating dichotic auditory stimulus was presented at the same frequency but with the phase varied to determine the temporal range over which the two stimuli were perceived as simultaneous at least 75% of the time, defined as the TBW. The mean TBW among younger subjects was 286 ms (SEM ± 56 ms) and among older subjects was 560 ms (SEM ± 52 ms). TBW was related to vestibular sensitivity among younger but not older subjects, suggesting that a prolonged TBW could be a mechanism for imbalance in the elderly person independent of changes in peripheral vestibular function.

Keywords: labyrinth/physiology; motion perception; proprioception/physiology; reaction time; rotation; sensory thresholds/physiology; time factors; vestibule.

Figure 1

Stimulus paradigm. Sinusoidal line represents the chair's position (negative values represent position to the left of center, positive values to the right). Dashed vertical lines represent auditory stimuli presented dichotically, with symbols above the horizontal line indicating sound presented in the right ear and those below the line indicating sounds presented in the left ear. In this example, the auditory stimulus occurs at a stimulus onset asynchrony of +125 ms following the time the chair's position reaches its extremes.

Figure 2

Psychometric curves from older ( A ) and younger ( B ) subjects. The x -axis represents the stimulus onset asynchrony in milliseconds, and the y -axis represents the proportion of times the stimuli were perceived as simultaneous. The green lines represent the psychometric curves and the closed circles represent each subject's actual response. The temporal binding window is contained between the set of red dashed lines, with the solid red line representing the point of subjective simultaneity.

Figure 3

Relationship of temporal binding window to the point of subjective simultaneity. Older subjects represented by open diamonds, younger subjects by closed squares.

Figure 4

Reliability analysis. The point of subjective simultaneity ( A ) and the temporal binding window ( B ) of younger (closed squares) and older (open diamonds) subjects. Time intervals of ∼4 days between testing sessions.