Psychophysical studies on the peri-saccadic perception of space, time, and object features

Sakkaden sind schnelle, ballistische Augenbewegungen. Trotz großer Unterschiede zwischen prä- und post-sakkadischen retinalen Abbildungen, erscheint die visuelle Wahrnehmung über Sakkaden hinweg als kontinuierlich und stabil. Zur Konstruktion dieser räumlichen und zeitlichen Stabilität sind aktive Kompensationsmechanismen notwendig. Unter Laborbedingungen sind die Grenzen dieser Kompensationsmechanismen aufzeigbar. In zeitlicher Nähe zu Sakkaden lassen sich spezifische, charakteristische Wahrnehmungsfehler nachweisen. In dieser Arbeit wurden psychophysische Experimente mit menschlichen Versuchspersonen zu Teilbereichen der zeitlichen und räumlichen, trans-sakkadischen Stabilität durchgeführt. Untersucht wurden dabei die peri-sakkadische Wahrnehmung von Zeit, die perzeptuellen Konsequenzen sakkadischer Adaptation, die peri-sakkadische Repräsentation von Objekteigenschaften sowie der Einfluss emotional relevanter Sakkadenziele

The interaction between human vision and eye movements in health and disease

Human motor behaviour depends on the successful integration of vision and eye movements. Many studies have investigated neural correlates of visual processing in humans, but typically with the eyes stationary and fixated centrally. Similarly, many studies have sought to characterise which brain areas are responsible for oculomotor control, but generally in the absence of visual stimulation. The few studies to explicitly study the interaction between visual perception and eye movements suggest strong influences of both static and dynamic eye position on visual processing and modulation of oculomotor structures by properties of visual stimuli. However, the neural mechanisms underlying these interactions are poorly understood. This thesis uses a range of fMRI methodologies such as retinotopic mapping, multivariate analsyis techniques, dynamic causal modelling and ultra high resolution imaging to examine the interactions between the oculomotor and visual systems in the normal human brain. The results of the experiments presented in this thesis demonstrate that oculomotor behaviour has complex effects on activity in visual areas, while spatial properites of visual stimuli modify activity in oculomotor areas. Specifically, responses in the lateral geniculate nucleus and early cortical visual areas are modulated by saccadic eye movements (a process potentially mediated by the frontal eye fields) and by changes in static eye position. Additionally, responses in oculomotor structures such as the superior colliculus are biased for visual stimuli presented in the temporal rather than nasal hemifield. These findings reveal that although the visual and oculomotor systems are spatially segregated in the brain, they show a high degree of integration at the neural level. This is consistent with our everyday experience of the visual world where frequent eye movements do not lead to disruption of visual continuity and visual information is seamlessly transformed into motor behaviour

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Mental and sensorimotor extrapolation fare better than motion extrapolation in the offset condition

Evidence for motion extrapolation at motion offset is scarce. In contrast, there is abundant evidence that subjects mentally extrapolate the future trajectory of weak motion signals at motion offset. Further, pointing movements overshoot at motion offset. We believe that mental and sensorimotor extrapolation is sufficient to solve the problem of perceptual latencies. Both present the advantage of being much more flexible than motion extrapolatio

Behavioural and neuronal correlates of visual saliency in mouse

While early parts of the brain’s sensory pathways convey signals about the entire environment, animal behaviour is usually devoted to one or just a few potential objects of interest at any given time. Objects that are more salient (more distinct) are usually prioritised, particularly if they are potential threats, but how and where salience is represented in the brain is not known. Here I examine how salience may be constructed in the visual pathways of mice. To highlight the importance of vision in mice I first show that vision can guide the selection of distinct defence behaviours in response to potential threats - freeze and flight. I then characterise potential neural mechanisms for salience, by making recordings from neurons in the superficial layers of the mouse superior colliculus, an area important in orienting behaviour towards- or away from objects and likely to be part of the salience circuit. I show that many of these neurons are sensitive to visual discontinuities in both the spatial and the temporal domain, and that this sensitivity is more pronounced in awake animals than in anesthetized animals. These results suggest that neurons in the mouse superior colliculus can highlight parts of the environment that are distinct from the spatial and temporal context that they are embedded in, and thus may help in directing animal behaviour with respect to salient objects

Time Course of Localization for a Repeatedly Flashing Stimulus Presented at Perisaccadic Timing

サッカード中に光点を連続点滅させると，Phantom Arnay (PA)と呼ばれる点線が知覚される。また，光点を縦1列に並べ，サッカード中に点滅バターンを高速で時間変化させると，点滅パターンが眼球運動により空間パターンに展開されて2次元イメージが知覚される．筆者らはこの現象を利用した視覚情報提示手法を提案してきた。この手法に基づいて情報提示を行う際に重要となるのが，知覚されるPAと眼球運動との時間関係である。そこで，本論文ではサッカード前中後を通して連続点滅する光点刺激の知覚と眼球運動との時間関係を，光点刺激を垂直方向に光らせ，光点知覚位置の時間変化を垂直方向の位置に置き換えることによって調べた．その結果，知覚された光点軌跡はサッカード開始とともにサッカードと逆方向に曲がり始め，サッカード終了とともに垂直方向に戻るものであり，相殺説から予測される光点軌跡とは異なるものであった