The phenomenology of pareidolia in healthy subjects and patients with left- or right-hemispheric stroke.

Pareidolia are perceptions of recognizable images or meaningful patterns where none exist. In recent years, this phenomenon has been increasingly studied in healthy subjects and patients with neurological or psychiatric diseases. The current study examined pareidolia production in a group of 53 stroke patients and 82 neurologically healthy controls who performed a natural images task. We found a significant reduction of absolute pareidolia production in left- and right-hemispheric stroke patients, with right-hemispheric patients producing overall fewest pareidolic output. Responses were categorized into 28 distinct categories, with 'Animal', 'Human', 'Face', and 'Body parts' being the most common, accounting for 72% of all pareidolia. Regarding the percentages of the different categories of pareidolia, we found a significant reduction for the percentage of "Body parts" pareidolia in the left-hemispheric patient group as compared to the control group, while the percentage of this pareidolia type was not significantly reduced in right-hemispheric patients compared to healthy controls. These results support the hypothesis that pareidolia production may be influenced by local-global visual processing with the left hemisphere being involved in local and detailed analytical visual processing to a greater extent. As such, a lesion to the right hemisphere, that is believed to be critical for global visual processing, might explain the overall fewest pareidolic output produced by the right-hemispheric patients.

Auditory spatial cueing reduces neglect after right-hemispheric stroke: A proof of concept study.

Spatial neglect after right-hemispheric stroke, characterized by the failure to attend or respond to the contralesional space, is a strong negative outcome predictor. Neglect is a supramodal syndrome affecting not only the visual but also the auditory modality. Preliminary studies used this audio-visual cross-modal effect to show short-lasting effects on attention towards the neglected space. The aim of the present study was to introduce a new technique of auditory stimulation combining the unspecific effect of music (i.e., patients choose their preferred music) with the effects of auditory spatial cueing (i.e., the music is presented dynamically as moving from right to left). The effect of this new auditory stimulation technique was investigated in two proof-of-concept experiments using repeated-measures, cross-over designs including 21 patients with visual neglect after a first right-hemispheric stroke. In Experiment I (n = 9), neglect patients showed a significantly larger improvement in Letter Cancellation after listening to preferred music with than without auditory spatial cueing. After granting the feasibility of this new auditory stimulation technique, we investigated the long-term aftereffects in Experiment II (n = 12). Herefore, we used video-oculography during Free Visual Exploration, a sensitive and reliable tool to assess spatial attention over time. Listening to music with auditory spatialcueing - as compared to music without auditory spatialcueing - significantly improved neglect severity in terms of visual exploration behaviour for up to 3h. A voxel-based-lesion-symptom mapping analysis over all patients revealed that the response variability in listening to music with auditory spatial cueing is determined by the integrity of the right inferior parietal lobule, the second branch of the superior longitudinal fascicle, and parieto-parietal callosal fibres. Our study shows that listening to music with auditory spatial cueing significantly reduces neglect severity and has the potential to be used as an add-on in the neurorehabilitation of neglect.

The spatial distribution of perseverations in neglect patients during a nonverbal fluency task depends on the integrity of the right putamen.

Deficient inhibitory control leading to perseverative behaviour is often observed in neglect patients. Previous studies investigating the relationship between response inhibition and visual attention have reported contradictory results: some studies found a linear relationship between neglect severity and perseverative behaviour whereas others could not replicate this result. The aim of the present study was to shed further light on the interplay between visual attention and response inhibition in neglect, and to investigate the neural underpinnings of this interplay. We propose the use of the Five-Point Test, a test commonly used to asses nonverbal fluency, as a novel approach in the context of neglect. In the Five-Point Test, participants are required to generate as many different designs as possible, by connecting dots within forty rectangles. We hypothesised that, because of its clear definition of perseverative errors, the Five-Point Test would accurately assess both visual attention as well as perseverative behaviour. We assessed 46 neglect patients with right-hemispheric stroke, and performed voxel-based lesion-symptom mapping (VLSM) to identify neural substrates of perseverative behaviour as well as the spatial distribution of perseverations. Our results showed that the Five-Point Test can reliably measure neglect and perseverative behaviour. We did not find any significant relationship between neglect severity and the frequency of perseverations. However, within the subgroup of neglect patients who displayed perseverative behaviour, the spatial distribution of perseverations significantly depended on the integrity of the right putamen. We discuss the putative role of the putamen as a potential subcortical hub to modulate the complex integration between visual attention and response inhibition processes.