Processing Low Spatial Frequencies Research Articles

Testing the magnocellular-pathway advantage in facial expressions processing for consistency over time

The ability to identify facial expressions rapidly and accurately is central to human evolution. Previous studies have demonstrated that this ability relies to a large extent on the magnocellular, rather than parvocellular, visual pathway, which is biased toward processing low spatial frequencies. Despite the generally consistent finding, no study to date has investigated the reliability of this effect over time. In the present study, 40 participants completed a facial emotion identification task (fearful, happy, or neutral faces) using facial images presented at three different spatial frequencies (low, high, or broad spatial frequency), at two time points separated by one year. Bayesian statistics revealed an advantage for the magnocellular pathway in processing facial expressions; however, no effect for time was found. Furthermore, participants’ RT patterns of results were highly stable over time. Our replication, together with the consistency of our measurements within subjects, underscores the robustness of this effect. This capacity, therefore, may be considered in a trait-like manner, suggesting that individuals may possess various ability levels for processing facial expressions that can be captured in behavioral measurements.

Socially anxious individuals discriminate better between angry and neutral faces, particularly when using low spatial frequency information

Background and objectivesSocial anxiety is associated with biased processing of threatening faces. Earlier research indicated that socially anxious individuals are biased towards processing low spatial frequency (LSF) information when judging facial expressions. However, it remains unclear whether this bias reflects better performance for LSF-information, worse performance for high spatial frequency (HSF) information that needs to be compensated for, or both. MethodsTo answer this question, we used frequency-filtered neutral and angry face stimuli in a speeded classification task to compare the performance of socially anxious and non-anxious individuals for different spatial frequency bands. ResultsAcross all spatial frequency bands, socially anxious individuals were faster in judging facial expressions. Importantly, this performance advantage was larger for LSF-filtered stimuli and most pronounced for those stimuli with the lowest frequency band. Analyzing inverse efficiency scores showed the same pattern, ruling out speed-accuracy trade-off differences between groups. LimitationsThe study uses rather artificial (bandpass-filtered) stimuli and is limited towards contrasting the discrimination of neutral and angry faces. Further, only participants with subclinical anxiety were part of the study, so clinical relevance remains to be shown. ConclusionsOur results show that social anxiety is not characterized by deficits in judging emotions from HSF-information, but by advantages when processing LSF-information.

Right-Hemisphere Specialization for Contour Grouping

Previous studies often revealed a right-hemisphere specialization for processing the global level of compound visual stimuli. Here we explore whether a similar specialization exists for the detection of intersected contours defined by a chain of local elements. Subjects were presented with arrays of randomly oriented Gabor patches that could contain a global path of collinearly arranged elements in the left or in the right visual hemifield. As expected, the detection accuracy was higher for contours presented to the left visual field/right hemisphere. This difference was absent in two control conditions where the smoothness of the contour was decreased. The results demonstrate that the contour detection, often considered to be driven by lateral coactivation in primary visual cortex, relies on higher-level visual representations that differ between the hemispheres. Furthermore, because contour and non-contour stimuli had the same spatial frequency spectra, the results challenge the view that the right-hemisphere advantage in global processing depends on a specialization for processing low spatial frequencies.

A distributed neural system for top-down face processing

Evidence suggests that the neural system associated with face processing is a distributed cortical network containing both bottom-up and top-down mechanisms. While bottom-up face processing has been the focus of many studies, the neural areas involved in the top-down face processing have not been extensively investigated due to difficulty in isolating top-down influences from the bottom-up response engendered by presentation of a face. In the present study, we used a novel experimental method to induce illusory face-detection. This method allowed for directly examining the neural systems involved in top-down face processing while minimizing the influence of bottom-up perceptual input. A distributed cortical network of top-down face processing was identified by analyzing the functional connectivity patterns of the right fusiform face area (FFA). This distributed cortical network model for face processing includes both “core” and “extended” face processing areas. It also includes left anterior cingulate cortex (ACC), bilateral orbitofrontal cortex (OFC), left dorsolateral prefrontal cortex (DLPFC), left premotor cortex, and left inferior parietal cortex. These findings suggest that top-down face processing contains not only regions for analyzing the visual appearance of faces, but also those involved in processing low spatial frequency (LSF) information, decision-making, and working memory.

Cerebral regions and hemispheric specialization for processing spatial frequencies during natural scene recognition. An event-related fMRI study

It has been suggested that visual scene recognition is mainly based on spatial frequency (Fourier) analysis of the image. This analysis starts with processing low spatial frequencies (LSF), followed by processing high spatial frequencies (HSF). Within the framework of the spatial frequency analysis, the right/left hemisphere would be predominantly involved in LSF/HSF analysis, respectively. The aim of this event-related fMRI study was to evaluate neural correlates and hemispheric specialization of spatial frequency analysis during recognition of nonfiltered (NF) and filtered, either in LSF or HSF, natural scenes. Comparing LSF or NF to HSF scene recognition, significant activation was obtained within right anterior temporal cortex and right parahippocampal gyrus. As these regions are known to be involved in scene processing, we interpret this result as suggesting that scene recognition is mainly based on LSF extraction and analysis. When LSF scene was compared to HSF scene recognition, supplementary activation was obtained within the right inferior parietal lobule that likely reflects attentional modulation on spatial frequency processing. A direct interhemispheric comparison for each particular band of spatial frequencies highlighted predominance within the early visual areas (such as the middle occipital gyrus) to the right for LSF processing and to the left for HSF processing. This result provides supplementary evidence for hemispheric specialization at early levels of visual analysis when spatial frequencies are processed.

Effects of background color on the global and local processing of hierarchically organized stimuli.

Recent studies have shown that (1) the global precedence effects in processing the hierarchically organized stimulus can be attenuated by eliminating the low spatial frequencies contained in the stimulus and (2) the human magnocellular pathway is responsible for processing low spatial frequencies and the pathway can be attenuated by imposing a red background on the stimulus. In the present study, a reaction-time experiment was conducted to examine the effect of background color of the stimulus to the processing of the hierarchically organized stimulus. The result showed that although the control condition (a green background) produced a prototypical asymmetric global interference, a red background that was equiluminant to the green background produced a symmetrical interference. It was concluded that the human magnocellular pathway is at least partially responsible in producing the global precedence effects.

Hemispheric processing of spatial frequencies in two commissurotomy patients

To test the hypothesis that in humans the left brain hemisphere is specialized for processing high spatial frequencies while the right hemisphere is specialized for processing low spatial frequencies, pairs of Gaussian windowed sinusoidal gratings were presented for 167 msec within the left and right visual fields of two commissurotomy patients. The gratings employed had spatial frequencies ranging from 1 to 8 cycles per degree, and horizontal or vertiaal orientations. The two gratings in each pair were identical in spatial frequency but could differ in orientation. Subjects reported if their orientations were the same or different. Twelve normal controls were also run. Accuracy data provides no indication of a relative advantage for high frequencies in the RVF or low frequencies in the LVF. One commissurotomy subject showed a trend in the reverse direction: the other was better with LVF presentations for all spatial frequencies. Control subjects failed to show a spatial frequency × visual field interaction. These outcomes suggest that at the processing stages required by the task, the hemispheres are not specialized for particular ranges of spatial frequencies.

Visual Pattern Recognition in the Cerebral Hemispheres: The Role of Spatial Filtering

The differences between the left and right cerebral hemispheres in terms of visual pattern recognition were examined within the context of the spatial filtering model of visual perception. On the basis of a wide range of evidence, it was hypothesized that the right hemisphere's predominant role in Gestalt perception may be related to its superiority in processing low spatial frequency information, while the left hemisphere may be more highly involved in an analysis of high frequency information contained in the visual environment. The spatial filtering capabilities of the left and right hemispheres were assessed by presenting square-wave gratings to the left and right visual fields, which project to the primary visual cortical areas of the contralateral hemispheres. 24 right-handed adult males were required to identify the orientation of each of six gratings varying in fundamental spatial frequency and level of contrast. Analyses of variance indicated that identification performance was superior over-all in the right visual field. The magnitude of the advantage of the right visual field latency was greater for the high frequency gratings, although this predicted trend did not attain significance. Results were discussed in relation to the spatial filtering theory and others concerning hemispheric differences in visual pattern recognition.