Research

My research focuses on visual perception under the presence of eye movements.

Post-saccadic visual dynamics

During natural viewing, humans constantly move their eyes, making several saccades per second. During fixation between saccades, the eye continues to make jitter-like movements known as drift. Both eye movements result in the discarding of redundant information in natural scenes (whitening), but the bandwidth of spatial frequencies affected by whitening differs [1-3]. Our experiment showed that the sensitivity to low spatial frequency started high immediately after a saccade, and further exposure was not beneficial at the center of gaze and led to minial improvement at larger eccentricities. On the other hand, sensitivity to high spatial frequency was low at first but continued to increase during post-saccadic fixation. Therefore, we show that luminance modulations from the natural saccade/drift cycle contribute to a global coarse-to-fine processing dynamics throughout the visual field. Saccades are responsible for establishing a visual gist, which is later enriched by fixational contributions.

Amplitude-dependent enhancement from saccades

This study takes a further step and looks at the luminance modulation of saccades with different amplitudes. The cut-off frequency of whitening depends on the velocity-amplitude profile of the saccade [4]. Therefore, a larger saccade delivers a more effective input than a smaller one below the critical frequency. We tested the perceptual consequences of this input reformatting by examining how large and small saccades affect contrast sensitivity. Empirical results closely follow theoretical predictions. Specifically, psychometric functions following small and large saccades only differed below the critical frequency of the former, in which case the larger saccade significantly enhanced the input strength. These results show that post-saccadic visibility critically depends on saccade amplitude.

Active control of saccades during signal detection

From the above studies, one exciting hypothesis is that we adapt different amplitudes of saccades as an active strategy in order to enhance the spatial frequencies of interest. We will test this by having subjects freely move their eyes while trying to detect signals with certian frequencies. Still in data collection.

Head and eye movements in natural vewing

Combine a high-resolution scleral search system with OptiTrack Motion Capture Systems [5]. We are able to record eye movements and head movements in a head free environment while subjects engage in all kinds of task such as threading a needle and visual search. This is a rich dataset and we are in active analysis on various fronts. For example, we have identified a task-dependent head-eye coordination during fixation [6].

Stereovision

The visual system can preceive small differences (binocular disparity) in the two eyes and compute the depth of objects [7-8]. This is an incredible ability, considering that the images of the two eyes are always in motion. How are diparities calculated in the presence of fixational eye movements (FEM)? We have tested it removing retinal image motion caused by FEM and by separating the consequences of different components of eye movements. The results show that the temporal modulation of disparity caused by eye movements are in fact beneficial for stereopsis.

References

[1] Kuang, X., Poletti, M., Victor, J.D., and Rucci, M. (2012). Temporal encoding of spatial nformation during active visual fixation. Current Biololgy, 22, 510–514.

[2] M. Rucci, E. Ahissar, and D. Burr, (2018) Temporal coding of visual space, Trends in Cognitive Sciences, 22(10): 883-895.

[3] Boi, M., Poletti, M., Victor, J. D., & Rucci, M. (2017). Consequences of the oculomotor ycle for the dynamics of perception. Current Biology, 27(9), 1268-1277

[4] Mostofi, N., Zhao, Z., Intoy, J., Boi, M., Victor, J. D., & Rucci, M. (2020). Spatiotemporal Content of Saccade Transients. Current Biology, 30(20), 3999- 4008.

[5] K. Eibenberger, B. Eibenberger and M. Rucci (2016). Design, simulation and evaluation of uniform magnetic field systems for head-free eye movement recordings with scleral search coils. IEEE Proc. Engineering in Medicine and Biology.

[6] Z. Zhao, Y. H. Li, R. Lin, S. Kapisthalam, A. M. Clark, B. Yang, J. Intoy, M. A. Cox, and M. Rucci (2022). Task-dependent head-eye coordination during natural fixation. Journal of Vision, 22(13).

[7] Cumming, B.G. & DeAngelis, G.C. (2001), The physiology of stereopsis. Annu. Rev. Neurosci., 24(1):203-238.

[8] DeAngelis, G.C. (2000), Seeing in three dimensions: the neurophysiology of stereopsis. Trends Cogn. Sci., 4(3):80-90