The effects of fixational tremor on the retinal image

The study of fixational eye motion (FEM) has implications for the neural and computational underpinnings of vision. One component of FEM is tremor, a high-frequency oscillatory jitter reported to be anywhere from ∼5 to 60 seconds of arc in amplitude. In order to isolate the effects of tremor on the retinal image directly and in the absence of optical blur, high-frequency, high-resolution eye traces were collected in 6 subjects from videos recorded with an Adaptive Optics Scanning Laser Ophthalmoscope. Videos were acquired while subjects engaged in an active fixation task where they fixated on a tumbling E stimulus and reported changes in its orientation. Spectral analysis was conducted on isolated segments of optical drift. The resultant amplitude spectra showed a slight deviation from the traditional 1/f nature of optical drift in the frequency range of 50-100 Hz, which is indicative of tremor; however, the amplitude of this deviation rarely exceeded one second of arc, smaller than any magnitude previously reported.