Temporal synchrony deficits in amblyopia.

PURPOSE: Amblyopia is a developmental abnormality of visual cortex characterized by spatial processing deficits. Recently, it has been suggested that temporal processing also is affected. We investigated temporal sensitivity by measuring temporal synchrony sensitivity.

METHODS

In Experiment 1, we used a contrast detection task to compare the detection of a flickering 3 Hz Gaussian blob to that of synchrony discrimination for a 180° phase shift. In Experiment 2, we measured synchrony thresholds directly by assessing the minimum degree of asynchrony that allowed subjects to discriminate which of 4 high-contrast Gaussian blobs was flickering asynchronously in time (synchrony thresholds). Three temporal frequencies (1, 2, and 3 Hz) and two element separations (1.25° and 5°) were compared.

RESULTS

In Experiment 1, we found that the amblyopes (mean age 19.90 ± 8.59 years, range 11-48 years) exhibited a synchrony deficit only for the 1.25 degrees element separation in the amblyopic eye. In Experiment 2, we also found that the sensitivity for nonstrabismic (pure anismetropia) amblyopes (mean age 15.70 ± 4.00 years, range 12-23 years) was reduced for all three temporal frequencies, whereas for strabismic (strabismus and anisometropia) amblyopes (mean age 24.10 ± 10.03 years, range 11-48 years) it was reduced at 3 Hz only, possibly suggesting a different extent of impairment in temporal synchrony for different types of amblyopia.

CONCLUSIONS

Our results suggest that amblyopes have a foveal low-level temporal processing deficit that could explain the previously reported deficit for figure-ground discrimination.