CONJUGACY OF SPONTANEOUS BLINKS IN MAN - EYELID KINEMATICS EXHIBIT BILATERAL SYMMETRY

Purpose. To provide a quantitative description of the conjugacy of hum an eyelid movements during spontaneous blinks. Methods. Eyelid movemen ts occurring during spontaneous blinks were recorded bilaterally using a modification of the electromagnetic search coil technique. In off-l ine analyses, covariation of amplitude, peak velocity, and duration of blink down phases were determined for the two eyelids. Interocular di fferences in the timing of blink onset and offset, and time to peak ve locity, also were evaluated. Results. Human blink motor control system s act to link tightly the spatial and temporal characteristics of move ments of die two eyelids. Data show that human spontaneous blinks are conjugate. Analysis of interocular covariation of blink amplitude, pea k velocity, and duration yielded linear functions with high correlatio n coefficients. Interocular comparison of eyelid movement durations du ring blinks showed a particularly high correlation. There were negligi ble interocular differences in blink down-phase onset time, terminatio n time, and time to peak velocity. A small percentage of blinks exhibi ted interocular differences in amplitude and peak velocity of >20%; ho wever, even in these cases, blink duration remained tightly linked. Co nclusion. Spatial and temporal properties of eyelid movements occurrin g during spontaneous blinks are conjugate. These data support the hypo thesis that a bilateral gating mechanism regulates blink duration. Ele ments downstream from the gate may differentially and unilaterally alt er blink amplitude and peak velocity, but the duration of blinks remai ns time-locked for the mio eyelids.