Effect of a concurrent counting task on dynamic visual accommodation

The visual accommodation of four male subjects was selectively recorded over a 3-day period using an objective, continuously recording, infrared optometer to determine the effects of a concurrent counting task on their ability to accommodate to a sinusoidally changing focus stimulus ranging from 0.0 to 3.0 D. There was an increase in their steady-state errors in the direction of negative accommodation of from 0.25 to 0.50 D, but the magnitude of the steady-state error induced by the concurrent task did not change over the three sine wave frequencies used (0.1, 0.2 and 0.4 Hz). The results are discussed in terms of an accommodative "lag" model of sympathetic-parasympathetic arousal induced by superimposing an extraneous mental task.