The Modulation of Haptic Line Bisection by a Visual Illusion and Optokinetic Stimulation

Multisensory enhancement elicited by unconscious visual stimuli

The merging of information from different senses (i.e., multisensory integration) can facilitate information processing. Processing enhancements have been observed with signals that are irrelevant to the task at hand, and with cues that are non-predictive. Such findings are consistent with the notion that multiple sensory signals are sometimes integrated automatically. Multisensory enhancement has even been reported with stimuli that have been presented subliminally, though only with meaningful multisensory relations that have already been learned. The question of whether there exist cases where multisensory effects occur without either learning or awareness has, though, not been clearly established in the literature to date. Here, we present a case study of a patient with Posterior Cortical Atrophy, who was unable to consciously perceive visual stimuli with our task parameters, yet who nevertheless still exhibited signs of multisensory enhancement even with unlearned relations between audiovisual stimuli. In a simple speeded detection task, both response speed, and the variability of reaction times, decreased in a similar manner to controls for multisensory stimuli. These results are consistent with the view that the conscious perception of stimuli and prior learning are not always a prerequisite for multisensory integration to enhance human performance.

The middle of the road: perceiving intermediates

This article aims to study the extension and immediacy of the perception of intermediates during the observation of images showing a variation in a spatial property from one extreme (e.g. at the top of a mountain) to the opposite extreme (e.g. at the bottom of a mountain). Three experiments were carried out: rating tasks were used in studies 1 and 3 and a classification task in study 2. Three main results emerged. The first result (concerning extension) is that people consistently recognize some instances of a dimension as intermediates (neither a… nor b) rather than as one or the other opposite pole (a, b). The number of these cases ranges from one to most of the experiences in between the two extremes, depending on the type of opposite considered. The second result (concerning immediacy) is that recognizing and rating intermediates did not take longer in most cases than recognizing and rating the two poles. The third result (concerning task influence) is that there were differences due to the type of task, i.e. rating and classification. The implications of these results are discussed within the framework of theories grounding cognition in perception.

The Oppel-Kundt illusion is effective in modulating horizontal space representation in humans

A modified version of the Oppel-Kundt illusion (i.e., a filled space is perceived as more expanded than an empty space of the same length) has been previously employed to distort space representation both in patients with neglect (i.e., failure to report/react to stimuli located in the space contralateral to the brain lesion) and in healthy participants. In those experiments, participants had to bisect or extend horizontal segments on backgrounds of exponentially spaced vertical lines. The exclusive use of visuo-motor tasks, however, did not allow excluding that the results were accounted for by a bias occurring at a response level of stimulus processing rather than by a visual illusion. To address this issue, in addition to a traditional line bisection task, a line length estimation task was employed, which allowed separating response and illusion-related factors. The results demonstrated that performance depended on the visual illusion rather than on a response bias. It was concluded that this version of the Oppel-Kundt illusion can be successfully employed to modulate space representation in humans.