Péter Csibri

Audio–visual integration through the parallel visual pathways

Audio-visual integration has been shown to be present in a wide range of different conditions, some of which are processed through the dorsal, and others through the ventral visual pathway. Whereas neuroimaging studies have revealed integration-related activity in the brain, there has been no imaging study of the possible role of segregated visual streams in audio-visual integration. We set out to determine how the different visual pathways participate in this communication. We investigated how audio-visual integration can be supported through the dorsal and ventral visual pathways during the double flash illusion. Low-contrast and chromatic isoluminant stimuli were used to drive preferably the dorsal and ventral pathways, respectively. In order to identify the anatomical substrates of the audio-visual interaction in the two conditions, the psychophysical results were correlated with the white matter integrity as measured by diffusion tensor imaging.The psychophysiological data revealed a robust double flash illusion in both conditions. A correlation between the psychophysical results and local fractional anisotropy was found in the occipito-parietal white matter in the low-contrast condition, while a similar correlation was found in the infero-temporal white matter in the chromatic isoluminant condition. Our results indicate that both of the parallel visual pathways may play a role in the audio-visual interaction.

Aging alters visual processing of objects and shapes in inferotemporal cortex in monkeys

Visual perception declines with age. Perceptual deficits may originate not only in the optical system serving vision but also in the neural machinery processing visual information. Since homologies between monkey and human vision permit extrapolation from monkeys to humans, data from young, middle aged and old monkeys were analyzed to show age-related changes in the neuronal activity in the inferotemporal cortex, which is critical for object and shape vision. We found an increased neuronal response latency, and a decrease in the stimulus selectivity in the older animals and suggest that these changes may underlie the perceptual uncertainties found frequently in the elderly.

Illusory flashes and perception.

Information from the environment can be based on a single or several modalities. The simultaneous processing of information separated in space and/or time depends on multiple factors. Visual illusions serve as a good tool with which to investigate the parallel processing of information and their interactions. This study was designed to gain information about a unimodal illusion: a target that flashes once seems to flash more as a result of a simultaneously presented inducer flashing several times nearby. The first aim of this work was to understand whether the number of perceived flashes is merely a result of a bias in the criterion level or whether it is based on a real percept. We then clarified how the illusion finds its way into the percept. The final step was designed to establish the logic of the processing in the background by determining whether the modality appropriateness hypothesis, the information reliability hypothesis, or the discontinuity theory best explains the predominant role of the inducer.

Virtual Out-of-Body Experience as a Potential Therapeutic Tool After Kidney Transplantation

The last wave of commercially available virtual reality (VR) devices opened ways to more immersive medical applications. We present a virtual reality system that exploits the virtual out-of-body experience to assist the acknowledgment of the transplanted body organ. We give an overview of the physiological background and set goals towards the VR system. An implementation using Oculus Rift hardware is presented. We describe the applied physiological evaluation process for kidney transplantation. The studies are currently still ongoing.

LCD Monitors as an Alternative for Precision Demanding Visual Psychophysical Experiments

Precise timing and presentation of stimuli is critical in vision research, still, the limiting factor in successful recognition is often the monitor itself that is used to present the stimuli. The most widespread method is the use of monitors controlled by personal computers. Traditionally, most experiments used cathode-ray tubes but they are more and more difficult to access, and instead, liquid–crystal displays are getting more and more popular. The two types have fundamentally different working principles and limitations in displaying the stimulus. In our experiments, the temporal precision of the stimulus presentation was in focus. We investigated whether liquid–crystal displays, which are not considered to be fit to display fast successive stimuli, can represent an alternative choice for cathode-ray tubes. We used the double flash and the flicker illusion to compare the technical capabilities of the two monitor types. These illusions not only do require a precise timing but also a very short exposure to the stimuli. At the same time, the interstimulus interval is also of extreme importance. In addition, these illusions require peripheral stimulation of the retina, which is more sensitive to the temporal aspects of the visual stimulus. On the basis of previous studies and our own psychophysical results, we suggest that liquid–crystal displays might be a good alternative for precise, frame-to-frame stimulus presentation even if parts of the stimuli are projected on the peripheral retina.

Contextual temporal features of the flash illusion

Simultaneous processing of pieces of information spread in space and/or in time depends on multiple factors [Chatterjee et al. 2011]. Studies regarding the effects of context on the visual target perception are generally addressing the spatial variables. For a deeper understanding of contextual effects in the temporal domain this study is aimed to gain information about one of the unimodal illusions called Phantom flashes. Here, a single target flash with multiple inducer flashes can be perceived as several flashes.