Can rotated words be processed automatically? Evidence from rotated repetition priming.

Visual word processing has its own dedicated neural system that, due to the novelty of this activity, is unlikely to have acquired its specialization through natural selection. Understanding the properties of this system could shed light on its recruitment and the background of its disorders. Although recognition of simple visual objects is orientation invariant, this is not necessarily the case for written words. We used a masked repetition priming paradigm to find out whether words retain their readability when viewed in atypical orientations. Subjects had to read out upright target words that were preceded by rotated prime words of the same or different identity. Priming duration was varied in Experiment 1 to assess the temporal emergence of a rotated priming effect. In Experiment 2, the letter order of the prime words was reversed in order to differentiate the processing stage where priming occurs. The orientational pattern of the priming effects seen in our results mostly confirms earlier word recognition models, but also serves a more detailed view about the effects of orientation on word form processing.

Transcranial Stimulation of the Orbitofrontal Cortex Affects Decisions about Magnocellular Optimized Stimuli.

Visual categorization plays an important role in fast and efficient information processing; still the neuronal basis of fast categorization has not been established yet. There are two main hypotheses known; both agree that primary, global impressions are based on the information acquired through the magnocellular pathway (MC). It is unclear whether this information is available through the MC that provides information (also) for the ventral pathway or through top-down mechanisms by connections between the dorsal pathway and the ventral pathway via the frontal cortex. To clarify this, a categorization task was performed by 48 subjects; they had to make decisions about objects' sizes. We created stimuli specific to the magno- and parvocellular pathway (PC) on the basis of their spatial frequency content. Transcranial direct-current stimulation was used to assess the role of frontal areas, a target of the MC. Stimulation did not bias the accuracy of decisions when stimuli optimized for the PC were used. In the case of stimuli optimized for the MC, anodal stimulation improved the subjects' accuracy in the behavioral test, while cathodal stimulation impaired accuracy. Our results support the hypothesis that fast visual categorization processes rely on top-down mechanisms that promote fast predictions through coarse information carried by MC via the orbitofrontal cortex.

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.

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.

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.