Decoding Trans-Saccadic Memory

Abstract

We examine whether peripheral information at a planned saccade target affects immediate postsaccadic processing at the fovea on saccade landing. Current neuroimaging research suggests that presaccadic stimulation has a late effect on postsaccadic processing, in contrast to the early effect seen in behavioral studies. Human participants (both male and female) were instructed to saccade toward a face or a house that, on different trials, remained the same, changed, or disappeared during the saccade. We used a multivariate pattern analysis of electroencephalography data to decode face versus house processing directly after the saccade. The classifier was trained on separate trials without a saccade, where a house or face was presented at the fovea. When the saccade target remained the same across the saccade, we could reliably decode the target 123 ms after saccade offset. In contrast, when the target was changed during the saccade, the new target was decoded at a later time-point, 151 ms after saccade offset. The "same" condition advantage suggests that congruent presaccadic information facilitates processing of the postsaccadic stimulus compared with incongruent information. Finally, the saccade target could be decoded above chance even when it had been removed during the saccade, albeit with a slower time course (162 ms) and poorer signal strength. These findings indicate that information about the (peripheral) presaccadic stimulus is transferred across the saccade so that it becomes quickly available and influences processing at its expected new retinal position (the fovea).SIGNIFICANCE STATEMENT Here we provide neural evidence for early information transfer across saccades. Specifically, we examined the effect of presaccadic sensory information on the initial neuronal processing of a postsaccadic stimuli. Using electroencephalography and multivariate pattern analysis, we found the following: (1) that the identity of the presaccadic stimulus modulated the postsaccadic latency of stimulus relevant information; and (2) that a saccadic neural marker for a saccade target stimulus could be detected even when the stimulus had been removed during saccade. These results demonstrate that information about the peripheral presaccadic stimulus was transferred across the saccade and influenced processing at a new retinal position (the fovea) directly after the saccade landed.

Keywords: electroencephalography; multivariate pattern analysis; trans-saccadic information.

Figure 1.

Saccade and fixation task stimulus. a, Fixation conditions. In both conditions, subjects fixate between the two dashed lines for 200 ms. An image (a house or a face) was then presented either centrally or 10° to the left of fixation for 500 ms. The black bar across eyes of the face is for publishing purposes only; the bar is not present in experimental stimuli. Participants are required to keep their fixation regardless of the position of the stimuli and report whether the image in trial n is the same or different to the image in trial n − 1. In this example only the face stimulus is shown; however, there was equal likelihood of the presentation of the house stimulus. b, Saccade conditions. In all conditions, participants fixate on the empty space between the two dashes. After 200 ms, an image was presented 10° to the left of the fixation point. The image could be a house or a face. Participants remain fixated on the fixation point while attending to the image for 500 ms until the fixation point disappears, which cued subjects to saccade to the image. In the same condition, participants' saccade would land on the same stimulus, whereas in the change condition participants' saccade would land on a different image. These images would be presented for 45 ms after saccade offset. In the disappear condition, the image would disappear as soon as the saccade was detected, so that the saccade would land on an empty space. Subjects were instructed to respond “same” if they landed on the same image, or “different” if they landed on the changed image.

Figure 2.

a, Peripheral training stimuli: classifier trained on 90% of peripheral fixation trials at each time-point individually and tested at each corresponding time-point with the remaining 10% of the trials. b, Central training stimuli: classifier trained on 90% of central fixation trials at each time-point individually and tested at each corresponding time-point with the remaining 10% of the trials. Note: the classification scales change from a to b. stim, Stimulation.

Figure 3.

Classification of the presaccadic time-period of saccade trials. Classifier trained on peripheral fixation conditions at each time-point and tested on the corresponding time-point within the presaccadic time-period from stimulation onset to 300 ms. The solid horizontal line indicates chance level (50%), 95% confidence intervals, and the Bonferroni-corrected p values depicted. Bonf, Bonferroni; stim, stimulation.

Figure 4.

Classification of postsaccadic time-period from saccade offset. The classifier was trained on the “fixation” condition trials with central stimuli. a, Classification performance between face and house for same saccade condition. b, Classification performance between face and house for the change condition. c, Classification performance between face and house for the disappear condition and “peripheral fixation” condition after stimulus offset (plus 51.5 ms to simulate saccade). The solid horizontal line indicates chance level (50%), and the vertical dotted line is the peak performance time-point of the fixation trials (140 ms), which is used to train the classifier. 95% confidence intervals and Bonferroni-corrected p values are depicted. Note that the classification performance scale is different for a/b and c. Bonf, Bonferroni; sacc, saccade; stim, stimulation.

Figure 5.

a, Training the classifier on each time-point of 90% of central fixation trials and test on every time-point of the remaining 10% of central fixation trials. b–d, Training the classifier on each time-point of central fixation trials and test on every time-point after saccade offset of the following: same trials (b), change trials (c), and disappear trials (d). Note that the range of classification performance changes in each panel.

Figure 6.

Using postsaccadic signals to train the classifier. a, Classification between same and change in postsaccadic time-period from the time-point corresponding to the mid-saccade transient in the change condition. The training classifier on each time-point of 90% of same and change trials and the test classifier on the corresponding time-point of the remaining 10% of same and change trials. b, Classify presaccadic EEG signal using postsaccadic traces. Classifier trained on peak decoding time-point in the postsaccadic time-period for each condition separately and then tested using the presaccadic time-period of the corresponding condition. Solid horizontal line indicates chance level (50%). 95% confidence intervals and Bonferroni-corrected p values are depicted. Bonf, Bonferroni.