12/24/2022 0 Comments Hemera lille![]() ![]() In realistic conditions of viewing, our visual system is exposed to a very large range of spatial frequencies and preferentially selects some spatial scales over others depending on temporal processing (e.g., exposure duration, Schyns and Oliva, 1994 Oliva and Schyns, 1997 Peyrin et al., 2006), task requirements (Schyns and Oliva, 1999 Peyrin et al., 2005), or distance of viewing (Brady and Oliva, 2012). Other studies have found a specific deficit of the processing of very low spatial frequencies (LSF), below 1.5 cycle/degree (Butler and Javitt, 2005 Revheim et al., 2006 Butler et al., 2007), which has been linked to subcortical magnocellular dysfunction (Butler and Javitt, 2005), although this interpretation remains controversial (Skottun and Skoyles, 2007).īeside their implication in early visual processing, spatial frequencies also play a role in the formation of coherent visual representations. Several studies suggest that this early processing may be dysfunctional in schizophrenia: for instance, patients have poorer performance in contrast sensitivity tasks at different spatial frequency ranges, compared to healthy controls (Slaghuis, 1998, 2004 Kéri et al., 2002 Butler et al., 2005, 2007 Revheim et al., 2006 Kéri and Benedek, 2007 Martínez et al., 2008 Kantrowitz et al., 2009). The detailed information contained in high spatial frequencies (HSF) is primarily processed by the parvocellular pathway (Kaplan and Shapley, 1986). The lowest spatial frequencies (below 1.5 cycle/degree) contain a coarse representation of the visual stimuli and are preferentially conveyed by the magnocellular pathway. Visual spatial frequencies are often considered as the atomic element of perception (Valois and Valois, 1990). It also impairs the processing of low level perceptual information such as spatial frequencies (Slaghuis, 1998 Butler et al., 2005). How do patients with schizophrenia use visual information to form a coherent representation of the world? Schizophrenia does not only impair high-level cognitive functions, such as executive functions (Dickinson et al., 2007), emotion recognition (Morris et al., 2009), or theory of mind (Sprong et al., 2007). This result may be interpreted as a dysfunction of the guidance of HSF processing by LSF processing. ![]() When a broad range of spatial frequencies are present in the image, as in normal conditions of viewing, patients preferentially rely on coarse visual information contained in LSF. The LSF preference found in schizophrenia confirms our previous study conducted with faces, and shows that this LSF bias generalizes to other categories of objects. However, both populations performed equally well with HSF and LSF filtered pictures in the control experiment, demonstrating that the LSF preference found with hybrid stimuli in patients was not due to an inability to perceive HSF. ![]() The results on the categorization task showed that patients chose more frequently LSF with hybrid stimuli compared to healthy controls. In a control experiment, participants performed the same task but with images of only a single object, either a LSF or HSF filtered animal or fruit, to verify that participants could perceive both HSF or LSF when presented in isolation. The reported category demonstrated which spatial scale was preferentially perceived in each trial. Observers were asked to report if they saw an animal or a fruit. These stimuli were single images consisting of two different objects, a fruit and an animal, each in a specific spatial frequency range, either low (LSF) or high (HSF). Here, 15 patients with schizophrenia and 11 healthy control adults performed a categorization task with hybrid stimuli. Given the ubiquity of faces in visual perception, it remains an open question whether the LSF bias is face specific or also occurs with other visual objects. In a previous work, we found that, compared to healthy volunteers, patients were biased toward low spatial frequencies (LSF) to identify facial expression at a glance. ![]() Studies have shown that patients with schizophrenia exhibit visual processing impairments, particularly regarding the processing of spatial frequencies. ![]()
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