Abstract
Visual motion processing is a well-established model system for studying neural population codes in primates. The common marmoset, a small new world primate, offers unparalleled opportunities to probe these population codes in key motion processing areas, such as cortical areas MT and MST, because these areas are accessible for imaging and recording at the cortical surface. However, little is currently known about the perceptual abilities of the marmoset. Here, we introduce a paradigm for studying motion perception in the marmoset and compare their psychophysical performance to human observers. We trained two marmosets to perform a motion estimation task in which they provided an analog report of their perceived direction of motion with an eye movement to a ring that surrounded the motion stimulus. Marmosets and humans exhibited similar trade-offs in speed vs. accuracy: errors were larger and reaction times were longer as the strength of the motion signal was reduced. Reverse correlation on the temporal fluctuations in motion direction revealed that both species exhibited short integration windows, however, marmosets had substantially less non-decision time than humans. Our results provide the first quantification of motion perception in the marmoset and demonstrate several advantages to using analog estimation tasks.
Footnotes
Supporting Information: None.
Our most significant revisions examine the role of fixational drift prior to saccades and its influence on the resulting perceptual decisions. We have included a new analysis (along with a new figure, Fig. 8) of small drift eye movements evoked during presentation of the motion stimulus. Fixational drift has a short latency from motion onset and low gain that is comparable to involuntary ocular following responses. We examined the extent to which fixational eye drift influences the subsequent saccade choices of motion direction. Consistent with recent studies in humans and macaque monkeys (e.g., Simoncini et al, 2012; Glasser and Tadin, 2014; Price and Blum, 2014), our results reveal a disassociation between the errors in the direction of drift eye movements and subjects choices, suggesting that the neural mechanisms supporting perceptual decisions and fixational drift eye movements are based on partly non-overlapping neural mechanisms.
