Centre-periphery-difference in low-level vision and its interactions with top-down and sensorimotor processes

There is a profound difference in low-level vision between the retinal centre and the periphery (cpd). That contrast sensitivity declines from centre to the periphery is well established in humans. However, recently TMS on FEF was found to remotely affect visual cortex such that the cpd was reduced. No direct connections between FEF and occipital visual areas are known, but connections between FEF, the pulvinar and the occipital visual areas exist. I examined the cpd pattern in contrast sensitivity after real lesions in FEF and pulvinar areas by estimating visual thresholds. The results showed that real lesions of FEF do not have the same effect as TMS and are consistent with TMS causing subthreshold activation mimicking covert visuospatial attention. The cpd pattern in contrast sensitivity was different between FEF and pulvinar patients. Differences were prominent for foveal processing, while peripheral processing revealed parallel deficits, although these did not reach significance. In the second part of this work I focused on manual visuo-motor processes that have been found to differ between centrally and peripherally presented subliminal primes. For the periphery, when invisible primes are compatible with targets in their motor associations, RT‟s to targets speed up. However, for foveal primes, priming costs (negative compatibility effects (NCE)) can occur with compatible primes and targets. I examined the impact of perceptual sensitivity decline for the absence of NCE in the periphery by equating primes‟ strength via contrast threshold measurements. The results showed that perceptual equation does not equate priming effects. The critical factor, to trigger visuo-motor processes in periphery was found to be the prolonged time of the mask-target interval (SOA). This indicates that the functionally distinct retinal areas can both trigger visuo-motor processes, which are independent from visibility equation.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

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

Centre-periphery-difference in low-level vision and its interactions with top-down and sensorimotor processes

There is a profound difference in low-level vision between the retinal centre and the periphery (cpd). That contrast sensitivity declines from centre to the periphery is well established in humans. However, recently TMS on FEF was found to remotely affect visual cortex such that the cpd was reduced. No direct connections between FEF and occipital visual areas are known, but connections between FEF, the pulvinar and the occipital visual areas exist. I examined the cpd pattern in contrast sensitivity after real lesions in FEF and pulvinar areas by estimating visual thresholds. The results showed that real lesions of FEF do not have the same effect as TMS and are consistent with TMS causing subthreshold activation mimicking covert visuospatial attention. The cpd pattern in contrast sensitivity was different between FEF and pulvinar patients. Differences were prominent for foveal processing, while peripheral processing revealed parallel deficits, although these did not reach significance. In the second part of this work I focused on manual visuo-motor processes that have been found to differ between centrally and peripherally presented subliminal primes. For the periphery, when invisible primes are compatible with targets in their motor associations, RT‟s to targets speed up. However, for foveal primes, priming costs (negative compatibility effects (NCE)) can occur with compatible primes and targets. I examined the impact of perceptual sensitivity decline for the absence of NCE in the periphery by equating primes‟ strength via contrast threshold measurements. The results showed that perceptual equation does not equate priming effects. The critical factor, to trigger visuo-motor processes in periphery was found to be the prolonged time of the mask-target interval (SOA). This indicates that the functionally distinct retinal areas can both trigger visuo-motor processes, which are independent from visibility equation

Assisting Navigation and Object Selection with Vibrotactile Cues

Our lives have been drastically altered by information technology in the last decades, leading to evolutionary mismatches between human traits and the modern environment. One particular mismatch occurs when visually demanding information technology overloads the perceptual, cognitive or motor capabilities of the human nervous system. This information overload could be partly alleviated by complementing visual interaction with haptics. The primary aim of this thesis was to investigate how to assist movement control with vibrotactile cues. Vibrotactile cues refer to technologymediated vibrotactile signals that notify users of perceptual events, propose users to make decisions, and give users feedback from actions. To explore vibrotactile cues, we carried out five experiments in two contexts of movement control: navigation and object selection. The goal was to find ways to reduce information load in these tasks, thus helping users to accomplish the tasks more effectively. We employed measurements such as reaction times, error rates, and task completion times. We also used subjective rating scales, short interviews, and free-form participant comments to assess the vibrotactile assisted interactive systems. The findings of this thesis can be summarized as follows. First, if the context of movement control allows the use of both feedback and feedforward cues, feedback cues are a reasonable first option. Second, when using vibrotactile feedforward cues, using low-level abstractions and supporting the interaction with other modalities can keep the information load as low as possible. Third, the temple area is a feasible actuation location for vibrotactile cues in movement control, including navigation cues and object selection cues with head turns. However, the usability of the area depends on contextual factors such as spatial congruency, the actuation device, and the pace of the interaction task

Incidental music: Enhancing the emotional experience of the audience

Environmental psychologists, like Robert Gifford who study transactions between individuals and their physical settings, maintain that as an individual\u27s environment is changed, the environment also changes his/her behavior and experience. (Gifford, 2002) Like other segments of a theatrical setting, manipulation of the environment can enhance or constrain a broad range of audience actions from traditional theatre audiences to shoppers in a mall or guests at a wedding. Physical elements, as well as other ambient factors such as lighting, color, and quality of materials, set design, music, fragrance, and room temperature are a sample of the dramatic elements used to orchestrate the environment. This paper explores the relationship between the elements utilized to create enhanced experiences in these different types of theatres and audiences through the introduction of incidental music to dramatic performance