Limits...
Saccade-induced image motion cannot account for post-saccadic enhancement of visual processing in primate MST.

Cloherty SL, Crowder NA, Mustari MJ, Ibbotson MR - Front Syst Neurosci (2015)

Bottom Line: Primates use saccadic eye movements to make gaze changes.In many visual areas, including the dorsal medial superior temporal area (MSTd) of macaques, neural responses to visual stimuli are reduced during saccades but enhanced afterwards.However, based on the timing of this effect, it may arise from a different mechanism than occurs in normal vision.

View Article: PubMed Central - PubMed

Affiliation: National Vision Research Institute, Australian College of Optometry Carlton, VIC, Australia ; Department of Optometry and Vision Sciences, Australian Research Council Centre of Excellence for Integrative Brain Function, University of Melbourne Parkville, VIC, Australia ; Department of Electrical and Electronic Engineering, University of Melbourne Parkville, VIC, Australia.

ABSTRACT
Primates use saccadic eye movements to make gaze changes. In many visual areas, including the dorsal medial superior temporal area (MSTd) of macaques, neural responses to visual stimuli are reduced during saccades but enhanced afterwards. How does this enhancement arise-from an internal mechanism associated with saccade generation or through visual mechanisms activated by the saccade sweeping the image of the visual scene across the retina? Spontaneous activity in MSTd is elevated even after saccades made in darkness, suggesting a central mechanism for post-saccadic enhancement. However, based on the timing of this effect, it may arise from a different mechanism than occurs in normal vision. Like neural responses in MSTd, initial ocular following eye speed is enhanced after saccades, with evidence suggesting both internal and visually mediated mechanisms. Here we recorded from visual neurons in MSTd and measured responses to motion stimuli presented soon after saccades and soon after simulated saccades-saccade-like displacements of the background image during fixation. We found that neural responses in MSTd were enhanced when preceded by real saccades but not when preceded by simulated saccades. Furthermore, we also observed enhancement following real saccades made across a blank screen that generated no motion signal within the recorded neurons' receptive fields. We conclude that in MSTd the mechanism leading to post-saccadic enhancement has internal origins.

No MeSH data available.


Related in: MedlinePlus

Enhancement of ocular following eye speed after real and simulated saccades and the effect of test direction. (A,B) Ocular following eye speed from one monkey for test stimuli presented after real saccades. In (A) the test stimuli were moving upward at 160°/s. Ocular following was robust for this test direction, and eye speed was significantly enhanced in the short-delay condition (blue) compared to the long-delay condition (gray). In (B) the test stimuli were moving downward at 160°/s. For this test direction ocular following was poor, with no evidence of post-saccadic enhancement. Ocular following was consistently poor for test stimuli moving in the downward direction. The remaining panels, (C–H), show ocular following eye speed for test stimuli moving at 160, 80, and 40°/s, averaged across all directions tested. Panels on the left [(C), 160°/s; (E), 80°/s; (G), 40°/s] show eye speed for test stimuli presented after real saccades. In all cases, ocular following eye speed was significantly enhanced in the short-delay condition (blue) compared to the long-delay condition (gray; ASL < 0.001). Panels on the right [(D), 160°/s; (F), 80°/s; (H), 40°/s] show corresponding ocular following eye speed for test stimuli presented after simulated saccades. Again, in each case ocular following eye speed was significantly enhanced in the short-delay condition (green) compared to the long-delay condition (gray; ASL < 0.001). In all panels, solid lines show eye speed signals averaged across all trials of a given speed and the shaded regions indicate ±1 SE, estimated by bootstrapping.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4555012&req=5

Figure 4: Enhancement of ocular following eye speed after real and simulated saccades and the effect of test direction. (A,B) Ocular following eye speed from one monkey for test stimuli presented after real saccades. In (A) the test stimuli were moving upward at 160°/s. Ocular following was robust for this test direction, and eye speed was significantly enhanced in the short-delay condition (blue) compared to the long-delay condition (gray). In (B) the test stimuli were moving downward at 160°/s. For this test direction ocular following was poor, with no evidence of post-saccadic enhancement. Ocular following was consistently poor for test stimuli moving in the downward direction. The remaining panels, (C–H), show ocular following eye speed for test stimuli moving at 160, 80, and 40°/s, averaged across all directions tested. Panels on the left [(C), 160°/s; (E), 80°/s; (G), 40°/s] show eye speed for test stimuli presented after real saccades. In all cases, ocular following eye speed was significantly enhanced in the short-delay condition (blue) compared to the long-delay condition (gray; ASL < 0.001). Panels on the right [(D), 160°/s; (F), 80°/s; (H), 40°/s] show corresponding ocular following eye speed for test stimuli presented after simulated saccades. Again, in each case ocular following eye speed was significantly enhanced in the short-delay condition (green) compared to the long-delay condition (gray; ASL < 0.001). In all panels, solid lines show eye speed signals averaged across all trials of a given speed and the shaded regions indicate ±1 SE, estimated by bootstrapping.

Mentions: In our experimental design the direction and speed of the test stimulus was determined by the tuning properties of the recorded neurons. It has been reported that ocular following is sensitive to both the speed and direction of the motion stimulus (Miles et al., 1986). Thus, while our stimuli were optimal for each recorded neuron, they were often sub-optimal for generating ocular following. Figure 4 shows ocular following responses from one animal in response to the test stimulus moving at a range of speeds. Figure 4A shows ocular following eye speed in response to a test stimulus moving upward (90°) at 160°/s, presented after real saccades. It is clear that initial ocular following eye speed is enhanced in the short-delay condition (blue) compared to the long-delay condition (gray; EI = 0.33, ASL < 0.001). However, we found that this enhancement was not evident for all test directions. For example, in the same animal ocular following was poor in response to the test stimulus moving in the opposite (270°, downward) direction, even for the same test speed of 160°/s. (Figure 4B). In fact, we consistently observed slower ocular following speeds and no post-saccadic enhancement for test stimuli moving in the downward direction. Nevertheless, Figures 4C–H show ocular following eye speed for three test speeds, 40, 80, and 160°/s, averaged across all directions tested. Panels on the left (Figures 4C,E,G) show ocular following eye speed for test stimuli presented after real saccades, while panels on the right (Figures 4D,F,H) show eye speed for test stimuli presented after simulated saccades. In all cases, initial ocular following eye speed is significantly enhanced in the short-delay condition compared to the long-delay condition (ASL < 0.001). Therefore, in contrast to the neural responses in MSTd, we found that enhancement of ocular following occurred after both real and simulated saccades.


Saccade-induced image motion cannot account for post-saccadic enhancement of visual processing in primate MST.

Cloherty SL, Crowder NA, Mustari MJ, Ibbotson MR - Front Syst Neurosci (2015)

Enhancement of ocular following eye speed after real and simulated saccades and the effect of test direction. (A,B) Ocular following eye speed from one monkey for test stimuli presented after real saccades. In (A) the test stimuli were moving upward at 160°/s. Ocular following was robust for this test direction, and eye speed was significantly enhanced in the short-delay condition (blue) compared to the long-delay condition (gray). In (B) the test stimuli were moving downward at 160°/s. For this test direction ocular following was poor, with no evidence of post-saccadic enhancement. Ocular following was consistently poor for test stimuli moving in the downward direction. The remaining panels, (C–H), show ocular following eye speed for test stimuli moving at 160, 80, and 40°/s, averaged across all directions tested. Panels on the left [(C), 160°/s; (E), 80°/s; (G), 40°/s] show eye speed for test stimuli presented after real saccades. In all cases, ocular following eye speed was significantly enhanced in the short-delay condition (blue) compared to the long-delay condition (gray; ASL < 0.001). Panels on the right [(D), 160°/s; (F), 80°/s; (H), 40°/s] show corresponding ocular following eye speed for test stimuli presented after simulated saccades. Again, in each case ocular following eye speed was significantly enhanced in the short-delay condition (green) compared to the long-delay condition (gray; ASL < 0.001). In all panels, solid lines show eye speed signals averaged across all trials of a given speed and the shaded regions indicate ±1 SE, estimated by bootstrapping.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4555012&req=5

Figure 4: Enhancement of ocular following eye speed after real and simulated saccades and the effect of test direction. (A,B) Ocular following eye speed from one monkey for test stimuli presented after real saccades. In (A) the test stimuli were moving upward at 160°/s. Ocular following was robust for this test direction, and eye speed was significantly enhanced in the short-delay condition (blue) compared to the long-delay condition (gray). In (B) the test stimuli were moving downward at 160°/s. For this test direction ocular following was poor, with no evidence of post-saccadic enhancement. Ocular following was consistently poor for test stimuli moving in the downward direction. The remaining panels, (C–H), show ocular following eye speed for test stimuli moving at 160, 80, and 40°/s, averaged across all directions tested. Panels on the left [(C), 160°/s; (E), 80°/s; (G), 40°/s] show eye speed for test stimuli presented after real saccades. In all cases, ocular following eye speed was significantly enhanced in the short-delay condition (blue) compared to the long-delay condition (gray; ASL < 0.001). Panels on the right [(D), 160°/s; (F), 80°/s; (H), 40°/s] show corresponding ocular following eye speed for test stimuli presented after simulated saccades. Again, in each case ocular following eye speed was significantly enhanced in the short-delay condition (green) compared to the long-delay condition (gray; ASL < 0.001). In all panels, solid lines show eye speed signals averaged across all trials of a given speed and the shaded regions indicate ±1 SE, estimated by bootstrapping.
Mentions: In our experimental design the direction and speed of the test stimulus was determined by the tuning properties of the recorded neurons. It has been reported that ocular following is sensitive to both the speed and direction of the motion stimulus (Miles et al., 1986). Thus, while our stimuli were optimal for each recorded neuron, they were often sub-optimal for generating ocular following. Figure 4 shows ocular following responses from one animal in response to the test stimulus moving at a range of speeds. Figure 4A shows ocular following eye speed in response to a test stimulus moving upward (90°) at 160°/s, presented after real saccades. It is clear that initial ocular following eye speed is enhanced in the short-delay condition (blue) compared to the long-delay condition (gray; EI = 0.33, ASL < 0.001). However, we found that this enhancement was not evident for all test directions. For example, in the same animal ocular following was poor in response to the test stimulus moving in the opposite (270°, downward) direction, even for the same test speed of 160°/s. (Figure 4B). In fact, we consistently observed slower ocular following speeds and no post-saccadic enhancement for test stimuli moving in the downward direction. Nevertheless, Figures 4C–H show ocular following eye speed for three test speeds, 40, 80, and 160°/s, averaged across all directions tested. Panels on the left (Figures 4C,E,G) show ocular following eye speed for test stimuli presented after real saccades, while panels on the right (Figures 4D,F,H) show eye speed for test stimuli presented after simulated saccades. In all cases, initial ocular following eye speed is significantly enhanced in the short-delay condition compared to the long-delay condition (ASL < 0.001). Therefore, in contrast to the neural responses in MSTd, we found that enhancement of ocular following occurred after both real and simulated saccades.

Bottom Line: Primates use saccadic eye movements to make gaze changes.In many visual areas, including the dorsal medial superior temporal area (MSTd) of macaques, neural responses to visual stimuli are reduced during saccades but enhanced afterwards.However, based on the timing of this effect, it may arise from a different mechanism than occurs in normal vision.

View Article: PubMed Central - PubMed

Affiliation: National Vision Research Institute, Australian College of Optometry Carlton, VIC, Australia ; Department of Optometry and Vision Sciences, Australian Research Council Centre of Excellence for Integrative Brain Function, University of Melbourne Parkville, VIC, Australia ; Department of Electrical and Electronic Engineering, University of Melbourne Parkville, VIC, Australia.

ABSTRACT
Primates use saccadic eye movements to make gaze changes. In many visual areas, including the dorsal medial superior temporal area (MSTd) of macaques, neural responses to visual stimuli are reduced during saccades but enhanced afterwards. How does this enhancement arise-from an internal mechanism associated with saccade generation or through visual mechanisms activated by the saccade sweeping the image of the visual scene across the retina? Spontaneous activity in MSTd is elevated even after saccades made in darkness, suggesting a central mechanism for post-saccadic enhancement. However, based on the timing of this effect, it may arise from a different mechanism than occurs in normal vision. Like neural responses in MSTd, initial ocular following eye speed is enhanced after saccades, with evidence suggesting both internal and visually mediated mechanisms. Here we recorded from visual neurons in MSTd and measured responses to motion stimuli presented soon after saccades and soon after simulated saccades-saccade-like displacements of the background image during fixation. We found that neural responses in MSTd were enhanced when preceded by real saccades but not when preceded by simulated saccades. Furthermore, we also observed enhancement following real saccades made across a blank screen that generated no motion signal within the recorded neurons' receptive fields. We conclude that in MSTd the mechanism leading to post-saccadic enhancement has internal origins.

No MeSH data available.


Related in: MedlinePlus