Cortical suppression during accommodation step responses

Abstract

Purpose: Step changes in accommodation from distance to near take approximately 500 ms, during which time it is uncertain what visual information we perceive. A process of visual suppression seems to occur as we do not notice any blurring. In the present study we examine the visual processing capabilities by measuring contrast sensitivity during accommodation responses. Methods: Contrast thresholds were measured for two viewing conditions (dynamic and static) using a 2‐alternative forced‐choice staircase procedure. Sinusoidal [1, 4 cycles per degree (cpd)] and square wave (9 cpd) gratings were presented on a monitor at 1 m for the duration of 26 ms. In the dynamic condition a 2 dioptre (1–3D) far to near accommodation step response (ASR) was induced while contrast threshold measurements were taken every 100 ms after onset of the ASR. Results were compared to measurements taken in the static condition, where steady state accommodation responses were induced for five stimulus distances ranging from 1 m–33 cm. Results: We found that contrast sensitivity in the high spatial frequency condition (9 cpd) was significantly reduced in dynamic compared with static conditions. Differences found between the dynamic and static thresholds at low and mid spatial frequencies (1, 4 cpd) were inconsistent. Conclusion: The results suggest that the visual system employs high spatial frequency suppression during ASRs in order to minimize blur. These findings support a theory of oculomotor control in which the various oculomotor subsystems have both fast and slow components. The fast component exhibits pre‐programming and suppression of fine spatial detail, while the slow component shows continuous feedback control.