Transcranial direct current stimulation of the right temporoparietal junction impairs third-person perspective taking

Given the current debates about the precise functional role of the right temporoparietal junction (rTPJ) in egocentric and exocentric perspective taking, in the present study we manipulated activity in the rTPJ to investigate the effects on a spatial perspective-taking task. Participants engaged in a mental body transformation task, requiring them to mentally rotate their own body to the position of an avatar, while undergoing anodal, cathodal, or sham transcranial direct current stimulation (tDCS) of the rTPJ. As a control task, participants judged the laterality of a stimulus feature with respect to a fixation cross on the screen. For the first half of the experiment (only during online tDCS), a task-selective effect of tDCS was observed, reflected in slower reaction times following anodal than following cathodal and sham tDCS for the mental body transformation task, but not for the control task. The effects of tDCS were most pronounced for stimuli implying a more difficult mental body transformation. No effects of tDCS were observed during the second half of the experiment. The effects of tDCS were most pronounced for participants scoring low on aberrant perceptual beliefs and spiritual transcendence, suggesting a relation between third-person perspective taking and bodily and perceptual experiences. The finding that anodal stimulation of the rTPJ impairs third-person perspective taking indicates a key role of this region in exocentric spatial processing.     

Note on Gibson's direct visual perception

Gibson's 'ecological approach to visual perception' is shown to be compatible with traditional memory-assisted perception, viz., if it is applied to automatic behavior.     

No effects of transcranial direct current stimulation on visual evoked potential and peak gamma frequency

Cognitive Processing - Evidence suggests that the visual evoked potential (VEP) and gamma oscillations elicited by visual stimuli reflect the balance of excitatory and inhibitory (E-I) cortical...     

Tactile stimulation disambiguates the perception of visual motion paths

Although visual perception traditionally has been considered to be impenetrable by non-visual information, there are a rising number of reports discussing cross-modal influences on visual perception. In two experiments, we investigated how coinciding vibrotactile stimulation affects the perception of two discs that move toward each other, superimpose in the center of the screen, and then move apart. Whereas two discs streaming past each other was the dominant impression when the visual event was presented in isolation, a brief coinciding vibrotactile stimulation at the moment of overlap biased the visual impression toward two discs bouncing off each other (Experiment 1). Further, the vibrotactile stimulation actually changed perceptual processing by reducing the amount of perceived overlap between the discs (Experiment 2), which has been demonstrated to be associated with a higher proportion of bouncing impressions. We propose that tactile-induced quantitative changes in the visual percept might alter the quality of the visual percept (from streaming to bouncing), thereby adding to the understanding of how cross-modal information interacts with early visual perception and how this interaction influences subsequent visual impressions.     

Distance perception and the ambiguity of visual stimulation: A theoretical note

Certain current views postulate that visual perception, especially of distance, is a function of optical stimulation alone. It is shown here that the optical array does not, in fact, specify absolute distance unambiguously, for either a stationary or a moving O. In view of this ambiguity of optical information, a more complex theory, comprising both visual and nonvisual information, as needed to explain, veridical perception.     

Mental imagery of visual motion modifies the perception of roll-vection stimulation

When viewing a wide-angle visual display, which rotates in the frontoparallel plane around the line of sight, observers experience an illusory shift of the direction of gravity; this shift leads to an apparent tilt of the body and displaces allocentric space coordinates. In this study, subjects adjusted an indicator to the apparent horizontal while viewing a rotating display. To determine whether top down processes could affect the illusion, the subjects were asked to visualize a rotating configuration of dots onto a blank central portion of the moving visual field. Visualizing dots and actually viewing the dots deflected the spatial judgment in very similar ways. These results demonstrate that top down processing can affect allocentric space coordinates.     

Anodal transcranial direct current stimulation of right temporoparietal area inhibits self-recognition

Self–other discrimination is a crucial mechanism for social cognition. Neuroimaging and neurostimulation research has pointed to the involvement of the right temporoparietal region in a variety of self–other discrimination tasks. Although repetitive transcranial magnetic stimulation over the right temporoparietal area has been shown to disrupt self–other discrimination in face-recognition tasks, no research has investigated the effect of increasing the cortical excitability in this region on self–other face discrimination. Here we used transcranial direct current stimulation (tDCS) to investigate changes in self–other discrimination with a video-morphing task in which the participant’s face morphed into, or out of, a familiar other’s face. The task was performed before and after 20 min of tDCS targeting the right temporoparietal area (anodal, cathodal, or sham stimulation). Differences in task performance following stimulation were taken to indicate a change in self–other discrimination. Following anodal stimulation only, we observed a significant increase in the amount of self-face needed to distinguish between self and other. The findings are discussed in relation to the control of self and other representations and to domain-general theories of social cognition.     

The effects of background visual roll stimulation on postural and manual control and self-motion perception

The effects of background visual roll stimulation on postural control, manual controlf andselfmotion perception were investigated in this study. In the main experiment, 8 subjects were exposed to wide field-of-view background scenes that were tilted and static, continuously rotating, or sinusoidally rotating at frequencies between 0.03 and 0.50 Hz, as well as a baseline condition. The subjects performed either a postural control task (maintain an upright stance) or a manual control task (keep an unstable central display horizontally level). Root-mean square (RMS) error in both the postural and manual control tasks was low in the static tilt condition and extremely high in response to continuous rotation. Although the phases of the postural and manual responses were highly similar, the power and RMS error generated by the sinusoidal visual background stimulation peaked at a lower frequency in the postural task. Vection ratings recorded at the end of the postural and manual trials somewhat paralleled tbafrequency tuning differences between tasks, which a subsequent experiment showed to be the result of the differential motion of the central display rather than the differential positioning of the subject. In general, these results show that the dynamic characteristics of visual orientation systems vary according to the specific motor and/or perceptual system investigated.     

Transcranial magnetic stimulation: neurophysiological applications and safety

TMS is a non-invasive tool for measuring neural conduction and processing time, activation thresholds, facilitation and inhibition in brain cortex, and neural connections in humans. It is used to study motor, visual, somatosensory, and cognitive functions. TMS does not appear to cause long-term adverse neurological, cardiovascular, hormonal, motor, sensory, or cognitive effects in healthy subjects. Single-pulse (<1Hz) TMS is safe in normal subjects. High frequency, high-intensity repetitive TMS (rTMS) can elicit seizures even in normal subjects. Safety guidelines for using rTMS have been published.     

Haptic and visual perception of roughness

In this study, we are interested in the following two questions: (1) how does perceived roughness correlate with physical roughness, and (2) how do visually and haptically perceived roughness compare? We used 96 samples of everyday materials, such as wood, paper, glass, sandpaper, ceramics, foams, textiles, etc. The samples were characterized by various different physical roughness measures, all determined from accurately measured roughness profiles. These measures consisted of spectral densities measured at different spatial scales and industrial roughness standards (R(a), R(q) and R(z)). In separate haptic and visual conditions, 12 na?ve subjects were instructed to order the 96 samples according to perceived roughness. The rank orders of both conditions were correlated with the various physical roughness measures. With most physical roughness measures, haptic and visual correspondence with the physical ordering was about equal. With others, haptic correspondence was slightly better. It turned out that different subjects ordered the samples using different criteria; for some subjects the correlation was better with roughness measures that were based on higher spatial frequencies, while others seemed to be paying more attention to the lower spatial frequencies. Also, physical roughness was not found to be the same as perceived roughness.     

A visual display system for reading and visual perception research

The selection of a computer visual display system suitable for word recognition and reading research is described. The software character generation routines permit flexible definition of character sets. The display software permits control of size scaling and point density of characters being displayed as well as control over the temporal microstructure of presenting and refreshing the displayed text.     

Eye movements and the integration of visual memory and visual perception

Because visual perception has temporal extent, temporally discontinuous input must be linked in memory. Recent research has suggested that this may be accomplished by integrating the active contents of visual short-term memory (VSTM) with subsequently perceived information. In the present experiments, we explored the relationship between VSTM consolidation and maintenance and eye movements, in order to discover how attention selects the information that is to be integrated. Specifically, we addressed whether stimuli needed to be overtly attended in order to be included in the memory representation or whether covert attention was sufficient. Results demonstrated that in static displays in which the to-be-integrated information was presented in the same spatial location, VSTM consolidation proceeded independently of the eyes, since subjects made few eye movements. In dynamic displays, however, in which the to-be-integrated information was presented in different spatial locations, eye movements were directly related to task performance. We conclude that these differences are related to different encoding strategies. In the static display case, VSTM was maintained in the same spatial location as that in which it was generated. This could apparently be accomplished with covert deployments of attention. In the dynamic case, however, VSTM was generated in a location that did not overlap with one of the to-be-integrated percepts. In order to "move" the memory trace, overt shifts of attention were required.