Re‐fixation and perseveration patterns in neglect patients during free visual exploration

Abstract

The literature suggests that neglect patients not only show impairments in directing attention toward the left, contralesional space, but also present with perseverative behavior. Moreover, previous studies described re‐fixations during visual search tasks, and interpreted this finding as an impairment of spatial working memory. The aim of the present study was to study re‐fixations and perseverations (i.e., recurrent re‐fixations to same locations) during free visual exploration, a task with high ecological validity. We hypothesized that: (1) neglect patient would perform re‐fixations more frequently than healthy controls within the right hemispace; and, (2) the re‐fixation behavior of neglect patients would be characterized by perseverative fixations. To test these hypotheses, we assessed 22 neglect patients and 23 healthy controls, measuring their eye movements during free exploration of naturalistic pictures. The results showed that neglect patients tend to re‐fixate locations within the ipsilesional hemispace when they freely explore naturalistic pictures. Importantly, the saliency of discrete locations within the pictures has a stronger influence on fixation behavior within the contralesional than within the ipsilesional hemispace in neglect patients. Finally, the results indicated that, for re‐fixations, saliency plays a more important role within the contralesional than the ipsilesional hemispace. Moreover, we found evidence that re‐fixation behavior of neglect patients is characterized by frequent recurrent re‐fixations back to the same spatial locations which may be interpreted as perseverations. Hence, with the present study, we could better elucidate the mechanism leading to re‐fixations and perseverative behavior during free visual exploration in neglect patients.

Visual Exploration Area in Neglect: A New Analysis Method for Video-Oculography Data Based on Foveal Vision

“…In all participants, video-oculography was used to assess visual fixation behavior during FVE, a paradigm that has reliably been used to assess visual attention allocation in space (Pflugshaupt et al, 2004;Ptak et al, 2009;Cazzoli et al, 2010Cazzoli et al, , 2011Osandón et al, 2012;Fellrath and Ptak, 2015;Delazer et al, 2018;Paladini et al, 2019). Hereby, 12 pictures of natural scenes or urban public places (full color, resolution of 1,200 × 900 pixels) and their 12 mirrored versions (mirrored along the vertical axis) were presented on a computer screen (Paladini et al, 2019). Each of the pictures was presented for 7 s. To enforce a common starting point of visual exploration for all participants, pictures were preceded by a central black fixation cross on a gray background, displayed for 1 s. All participants were instructed to freely explore the pictures and to fixate on the central fixation cross presented between pictures.…”

“…Four conventional analyses, aimed at quantifying neglect severity, were performed: (1) mean horizontal gaze position, reflecting the center of mass of the spatial distribution of visual fixations on the horizontal axis during FVE (e.g., Paladini et al, 2019). The mean horizontal gaze position was calculated in degrees of visual angle from the center of the picture (0 = perfectly aligned with the horizontal middle of the picture; negative values = mean horizontal gaze position within the left half of the screen; positive values = mean horizontal gaze position within the right half of the screen); (2) horizontal position of the leftmost visual fixation (in degrees of visual angle from the center of the picture), reflecting the maximum leftward extensions of the FVE field (e.g., Dijkerman et al, 2003); (3) mean number of fixations in the left and right halves of the screen, reflecting the numerical distribution of fixations in the left and right FVE fields (e.g., Pflugshaupt et al, 2004;Paladini et al, 2019); and (4) mean cumulative fixation duration in the left and right halves of the screen, reflecting the time spent in the left and right FVE fields (e.g., Pflugshaupt et al, 2004;Cazzoli et al, 2009).…”

“…A further advantage of the proposed approach, based on fixation areas rather than points, could be that the percentage of single and overlapping fixations can easily be assessed. Indeed, it has recently been shown that neglect patients produce several fixations on nearby coordinates during FVE, whereas this phenomenon is significantly less pronounced in healthy subjects (Paladini et al, 2019). Hence, particularly, in neglect patients, the fixation areas may overlap.…”

“…After stroke, neglect has been reported to occur in 43-80% of patients with a right-hemispheric lesion and in 20-62% of patients with a left-hemispheric lesion (Stone et al, 1991;Azouvi et al, 2002;Ringman et al, 2004). Recently, video-oculography during free visual exploration (FVE) has been shown to be a valuable and reliable tool to evaluate visual attention allocation in neglect patients (Pflugshaupt et al, 2004;Ptak et al, 2009;Cazzoli et al, 2010Cazzoli et al, , 2011Osandón et al, 2012;Fellrath and Ptak, 2015;Delazer et al, 2018;Ohmatsu et al, 2019;Paladini et al, 2019).…”

“…For instance, the spatial distribution of visual fixations along the horizontal axis (assessed by means of the mean gaze position and the mean number of fixations within a given portion of the exploration field) is typically shifted toward the ipsilesional screen half in neglect patients as compared to healthy controls. Also, an ipsilesional bias is observed when the time spent within each screen half or the position of the leftmost fixation is considered (e.g., Dijkerman et al, 2003;Pflugshaupt et al, 2004;Cazzoli et al, 2009;Ohmatsu et al, 2019;Paladini et al, 2019).…”