Update: The paper is now out and available here:
This is the key paper of Lisa’s PhD. While decades of research have characterized pre-saccadic sensitivity modulations at the target of eye movements, little is known about the concurrent development of visual sensitivity in the pre-saccadic center of gaze. In a series of experiments, we demonstrate that pre-saccadic foveal processing operates predictively: defining features of an eye movement target (in our case its orientation) are enhanced at the pre-saccadic fixation location. We presented large-field pink noise images in rapid succession (20 Hz). Observers maintained fixation in the screen center and, upon detecting an orientation-filtered patch in their periphery (the target), started preparing an eye movement towards it. At some point during saccade preparation, a second orientation-filtered patch (the probe) appeared foveally on 50% of trials. If present, the probe either had the same orientation as the saccade target (congruent) or a different orientation (incongruent). Observers indicated if the foveal probe had been present or absent. After generating a ‘present’ response, they additionally reported the perceived orientation of the probe.
We made five main observations.
- Observers’ responses suggest foveal enhancement of the target orientation. Hit Rates (HRs) for target-congruent foveal probes started to exceed incongruent HRs 175 ms before saccade onset.
- In our design, the foveal region was never void of signal but contained incidental orientation information in the background noise even on probe absent trials. On such trials, we expected observers to become sensitive to target-congruent orientations in the foveal noise and, hence, to report the target’s orientation more often than the orthogonal orientation. Indeed, congruent False Alarm rates (FARs) exceeded incongruent ones. We determined the characteristics of all background noise images that had been presented when a congruent or incongruent FA was generated. For observers to perceive the target in the foveal noise (congruent FA), a high energy around the target orientation was required. Perceiving the non-target orientation required both, evidence for this orientation and an absence of evidence for the target orientation. In other words, the foveal noise had to look as target-dissimilar as possible for observers to report a competing orientation.
- Enhancement was spatially confined to the center of gaze and its immediate vicinity. By densely sampling the (para-)foveal space, we show that enhancement peaks in the center of gaze & exhibits an asymmetric profile, extending further towards than away from the target. The lack of parafoveal enhancement is not caused by lower visual performance at larger eccentricities. We did not observe enhancement at ±3 dva eccentricity even after raising parafoveal performance to a foveal level by adaptively increasing probe opacity.
- Foveal prediction is not a simple correlate of predictive remapping: Enhancement was aligned to the center of gaze, not to the predictively remapped location of the saccade target. Check out Figure 3 in the paper for details!
- Foveal enhancement during saccade preparation is more pronounced and emerges faster than foveal enhancement during passive fixation. Based on these findings, we suggest a crucial contribution of foveal processing to trans-saccadic visual continuity: Foveal processing of saccade targets commences before the movement is executed and enables a seamless transition once the center of gaze reaches the target.