Coarse-to-fine encoding of spatial frequency information into visual short-term memory for faces but impartial decay.

Face perception studies investigated how spatial frequencies (SF) are extracted from retinal display while forming a perceptual representation, or their selective use during task-imposed categorization. Here we focused on the order of encoding low-spatial frequencies (LSF) and high-spatial frequencies (HSF) from perceptual representations into visual short-term memory (VSTM). We also investigated whether different SF-ranges decay from VSTM at different rates during a study-test stimulus-onset asynchrony. An old/new VSTM paradigm was used in which two broadband faces formed the positive set and the probes preserved either low or high SF ranges. Exposure time of 500 ms was sufficient to encode both HSF and LSF in the perceptual representation (experiment 1). Nevertheless, when the positive-set was exposed for 500 ms, LSF-probes were better recognized in VSTM compared with HSF-probes; this effect vanished at 800-ms exposure time (experiment 2). Backward masking the positive set exposed for 800 ms re-established the LSF-probes advantage (experiment 3). The speed of decay up to 10 seconds was similar for LSF- and HSF-probes (experiment 4). These results indicate that LSF are extracted and consolidated into VSTM faster than HSF, supporting a coarse-to-fine order, while the decay from VSTM is not governed by SF. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Revisiting the role of spatial frequencies in the holistic processing of faces.

V. Goffaux and B. Rossion (2006) argued that holistic processing of faces is largely supported by low spatial frequencies (LSFs) but less so by high spatial frequencies (HSFs). We addressed this claim using a sequential matching task with face composites. Observers judged whether the top halves of aligned or misaligned composites were identical. We replicated the V. Goffaux and B. Rossion (2006) results, finding a greater alignment effect in accuracy for LSF compared with HSF faces on same trials. However, there was also a greater bias for responding "same" for HSF compared with LSF faces, indicating that the alignment effects arose from differential response biases. Crucially, comparable congruency effects found for LSF and HSF suggest that LSF and HSF faces are processed equally holistically. These results demonstrate that it is necessary to use measures that take response biases into account in order to fully understand the holistic nature of face processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contour integration across spatial frequency.

Association field models of contour integration suggest that local band-pass elements are spatially grouped to global contours within limited bands of spatial frequency (Field, Hayes, & Hess, 1993). While results for local orientation and spacing variation render support for AF models, effects of spatial frequency (SF) have rarely been addressed. To explore whether contour integration occurs across SF, we studied human contour detection in Gabor random fields with SF jitter along the contour, and in the embedding field. Results show no impairment of contour detection when the contour elements are 1.25 octaves apart. Even with a SF separation of 2.25 octaves there is only moderate impairment. Because SF tuning functions measured for contextual interactions of neighbored single band-pass elements indicate much smaller bandwidths (Polat & Sagi, 1993), the results imply that contour integration cannot rest solely on local locking among neighbored orientation and SF tuned mechanisms. Robustness across spatial frequency, and across color and depth, as found recently, indicates that local orientation based grouping integrates across other basic features. This suggests an origin in not too distal brain regions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attentional persistence for features of hierarchical patterns.

Priming for perceptual wholes and parts was examined in 4 experiments involving patterns arranged in a spatial hierarchy (D. Navon, see record 1978-11488-001). Previous studies have demonstrated "level-specific priming" across successive trials for these patterns (L. C. Robertson et al, see record 80:40200; L. M. Ward, see record 69:02582), and studies in neuropsychology have shown an absence of this priming effect in patient groups with parietal damage (R. Rafal & L. M. Robertson, 1995). The present experiments demonstrate that level-specific priming is linked to the spatial frequency differences between global and local forms in hierarchical patterns. They also show that level-specific priming is present even when the stimulus as a whole changes location. The effects last for up to 3 sec without diminution and are not affected by changes in color, polarity, or contrast. These findings are discussed as they relate to spatial attention, object perception, and memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attention allocation modulates the processing of hierarchical visual patterns: A comparative analysis of capuchin monkeys (Cebus apella) and humans.

Humans show a global advantage when processing hierarchical visual patterns, and they detect the global level of stimulus structure more accurately and faster than the local level in several stimulus contexts. By contrast, capuchins (Cebus apella) and other monkey species show a strong local advantage. A key factor which, if manipulated, could cause an inversion of this effect in monkeys is still to be found. In this study, we examined whether it was possible to induce attention allocation to global and local levels of perceptual analysis in capuchin monkeys and if by doing so, their local dominance could be reversed. We manipulated attentional bias using a matching-to-sample (MTS) task where the proportion of trials requiring global and local processing varied between conditions. The monkeys were compared with humans tested with the same paradigm. Monkeys showed a local advantage in the local bias condition but a global advantage in the global bias condition. The role of attention in processing was confined to the local trials in a first phase of testing but extended to both local and global trials in the course of task practice. Humans exhibited an overall global dominance and an effect of attentional bias on the speed of processing of the global and local level of the stimuli. These results indicate a role for attention in the processing of hierarchical stimuli in monkeys and are discussed in relation to the extent to which they can explain the differences between capuchin monkeys and humans observed in this and other studies. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Dominance of global visual properties at birth.

Six experiments are reported that were aimed at demonstrating the presence in newborns of a perceptual dominance of global over local visual information in hierarchical patterns, similar to that observed in adults (D. Navon, 1977, 1981). The first four experiments showed that, even though both levels of visual information were detectable by the newborn (Experiments 1A and 1B), global cues enjoyed some advantage over local cues (Experiments 2 and 3). Experiments 4A and 4B demonstrated that the global bias was strictly dependent on the low spatial frequency content of the stimuli and vanished after selective removal of low spatial frequencies. The results are interpreted as suggesting parallels between newborns' visual processing and processing later in development. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hemispheric asymmetries for global and local visual perception: Effects of stimulus and task factors.

Although neurological and physiological studies indicate a right hemisphere superiority in global processing and a left hemisphere superiority in local processing of Navon-type hierarchical letters (D. Navon, 1977), most investigations of lateralized perception in healthy participants report neither asymmetry. In 6 experiments the authors examined the influence of attentional demands, stimulus properties, and mode of response on perceptual asymmetries for global and local perception. Consistent with their theoretical predictions, asymmetries were more robust on divided- than focused-attention tasks and in response to stimuli in which local and global levels were equally salient compared with those with greater global than local saliency. Contrary to their prediction, perceptual asymmetries were not influenced by the complexity of the motor response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Competition and sharing of processing resources in visual discrimination.

Discrimination thresholds for spatial frequency and contrast tested individually were compared with dual discrimination of contrast and spatial frequency, and dual discrimination of 2 contrast or spatial frequency components. The components were presented overlapping, forming a compound grating or as side-by-side simple gratings. When observers had to judge contrast and spatial frequency simultaneously, discrimination thresholds increased by an amount predicted by a model of stimulus uncertainty for orthogonal dimensions (1.7); when they had to judge 2 frequency or contrast components, discrimination thresholds increased by a factor of 3–6 compared with the single-judgment task. The relative spatial location of the components did not interact with task complexity. The results are consistent with a model assuming a set of parallel special-purpose attentional mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Global and local processing in nonattended objects: A failure to induce local processing dominance.

L. Paquet and P. M. Merikle (1988) found that Ss can ignore the category of unattended local forms but not that of global forms. Does this finding reflect a priority for global information during perception? In 5 studies, 2 compound stimuli, each surrounded by a frame, were presented side by side, and attention was directed to 1 of the stimuli. The 1st 2 studies examined whether local dominance would emerge if a small gap (Exp 1) or the presence of small white lines (Exp 2) on the surrounding frame specified the target object. No evidence for local dominance was found. Three additional studies examined whether local dominance would be obtained if Ss had extensive practice identifying the local aspect of stimulus displays. Although local practice led to automatic detection of unattended local targets, it did not affect the processing of the global aspect. These results are proposed to exemplify the priority of global information during perception. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Primacy of wholistic processing and global/local paradigm: A critical review.

The question of whether perception is analytic or wholistic is an enduring issue in psychology. The global-precedence hypothesis, considered by many as a modern version of the Gestaltist claim about the perceptual primacy of wholes, has generated a large body of research, but the debate still remains very active. This article reviews the research within the global/local paradigm and critically analyzes the assumptions underlyling this paradigm. The extent to which this line of research contributes to understanding the role of wholistic processing on object perception is discussed. It is concluded that one should be very cautious in making inferences about wholistic processing from the processing advantage of the global level of stimulus structure. A distinction is proposed between global properties, defined by their position in the hierarchical structure of the stimulus, and wholistic properties, defined as a function of interrelations among component parts. It is suggested that a direct comparison between processing of wholistic and component properties is needed to support the hypothesis about the perceptual primacy of wholistic processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neural mechanisms of global and local processing. A combined PET and ERP study

The neural mechanisms of hierarchical stimulus processing were investigated using a combined event-related potentials (ERPs) and positron emission tomography (PET) approach. Healthy subjects were tested under two conditions that involved selective or divided attention between local and global levels of hierarchical letter stimuli in order to determine whether and where hemispheric differences might exist in the processing of local versus global information. When attention was divided between global and local levels, the N2 component of the ERPs (260- to 360-msec latency) elicited by the target stimuli showed asymmetries in amplitude over the two hemispheres. The N2 to local targets was larger over the left hemisphere, but the N2 to global targets tended to be slightly larger over the right hemisphere. However, the shorter-latency, sensory-evoked P1 component (90- to 150-msec latency) was not different for global versus local targets under conditions of divided attention. In contrast, during selective attention to either global or local targets, asymmetries in the N2 component were not observed. But under selective attention conditions, the sensory-evoked P1 components in the extrastriate cortex were enlarged for global versus local attention. Increased regional cerebral blood flow in the posterior fusiform gyrus bilaterally was observed in the PET data during selective attention to either global or local targets, but neither these nor the P1 component showed any tendency toward hemispheric difference for global versus local attention. Neither were there any activations observed in the parietal lobe during selective attention to global versus local targets. Together these data indicate that early sensory inputs are not modulated to gate global versus local information differentially into the two hemispheres. Rather, later stages of processing that may be asymmetrically organized in the left and right hemispheres operate in parallel to process global and local aspects of complex stimuli (i.e., the N2 effect of the ERPs). This pattern of results supports models proposing that spatial frequency analysis is only asymmetric at higher stages of perceptual processing and not at the earliest stages of visual cortical analysis.     

Effects of cue context on the perception of depth from combined disparity and perspective cues

PURPOSE: In normal vision, stereoscopic cues are combined with perspective cues to provide veridical depth perception. The relative strengths of these depth cues, however, may be dependent upon context effects. We investigated the role of stimulus context on the interactions of binocular disparity, contrast, and size. METHODS: The subjects, four observers with normal stereoacuity and one stereo-amblyope, discriminated far vs. near perceived depth of Gabor patches; feedback was based on the sign of binocular disparity. Depth discrimination functions were measured under conditions in which depth cues were consonant or in conflict. Three stimulus contexts were used: (1) variable disparity with fixed spatial frequency and contrast; (2) variable contrast with fixed spatial frequency and disparity; and (3) variable spatial frequency with fixed contrast and disparity. The effects of stimulus context were derived from comparisons of discrimination rates for identical stimuli across the three sets of conditions. RESULTS: In subjects with normal stereopsis, for disparities less than 2 arcmin, depth perception was dominated by contrast in contrast-varying sessions, or by size in spatial frequency-varying sessions. With larger disparities, depth perception became dependent on disparity, regardless of the contrast or spatial frequency of the test stimulus. The results for the stereo-amblyope showed much greater dependence on perspective cues and, in most cases, the transition from perspective- to disparity-based depth perception did not occur. CONCLUSIONS: These investigations demonstrate strong stimulus context effects and have important implications for the combination rules of stereoscopic and perspective cues in depth perception of normal and stereo-deficient subjects.     

Contextual modulation of the motion aftereffect.

The authors examined center-surround effects for motion perception in human observers. The magnitude of the motion aftereffect (MAE) elicited by a drifting grating was measured with a nulling task and with a threshold elevation procedure. A surround grating of the same spatial frequency, temporal frequency, and orientation significantly reduced the magnitude of the MAE elicited by adaptation to the center grating. This effect was bandpass tuned for spatial frequency, orientation, and temporal frequency. Plaid surrounds but not contrast-modulated surrounds that moved in the same direction also reduced the MAE. These results provide psychophysical evidence for center-surround interactions analogous to those previously observed in electrophysiological studies of motion processing in primates. Collectively, these results suggest that motion processing, similar to texture processing, is organized for the purpose of highlighting regions of directional discontinuity in retinal images. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cellular basis for the negative dromotropic effect of adenosine on rabbit single atrioventricular nodal cells

Detection and resolution of square patches of sinusoidal gratings were measured in central and peripheral vision (30 degrees horizontal temporal visual field) for high-contrast gratings as a function of the number of cycles in the stimulus. We determined performance in a forced-choice paradigm for a fixed number of stimulus cycles by arranging for stimulus diameter to vary inversely with spatial frequency. For both psychophysical tasks and for both target locations, the psychometric function relating performance to log spatial frequency shifted to higher frequencies without changing slope significantly as the number of cycles in the stimulus was increased. Thus the entire effect could be captured by an analysis of spatial acuity, which increased with increasing number of grating cycles over the range 0.5-6 cycles but remained constant over the range 6-14 cycles. In the central field, resolution acuity and detection acuity were equal regardless of the number of cycles in the stimulus. In the peripheral field, detection acuity exceeded resolution acuity and perceptual aliasing occurred for stimuli in the range 1-14 cycles. From this result we conclude that resolution acuity is sampling limited in the periphery, provided that the stimulus contains at least one full cycle of the grating. Essential features of the results could be accounted for by Fourier analysis of the stimulus.     

Global and local processing in humans (Homo sapiens) and chimpanzees (Pan troglodytes): Use of a visual search task with compound stimuli.

This research assessed the visual processing of the global and local stimulus features in humans and chimpanzees. In Experiment 1, participants were tested with compound stimuli presented in a visual search task. There was an advantage to process the global stimulus level in humans but not in chimpanzees. The global size and the density of the local elements were manipulated in Experiment 2. Humans showed an overall advantage for processing the global shape. Chimpanzees showed an advantage for processing the local shape in the low-density condition but showed no advantage in the dense conditions. In Experiment 3, chimpanzees showed a global advantage when line segments connected the local elements and a local one when the lines were removed. Together, these results suggest a phylogenetic trend in the way compound stimuli are processed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of a lateralized parietal-basal ganglia circuit in hierarchical pattern perception: Evidence from Parkinson's disease.

The role of corticostriatal circuits in hierarchical pattern perception was examined in Parkinson's disease. The hypothesis was tested that patients with right-side onset of motor symptoms (RPD, left hemisphere dysfunction) would be impaired at local level processing because the left posterior temporoparietal junction (TP) emphasizes processing of local information. By contrast, left-side onset patients (LPD; right hemisphere dysfunction) would show impaired global processing because right TP emphasizes global processing. Participants identified targets at local or global levels without and with attention biased toward those levels. Despite normal attentional control between levels, LPD patients showed a single dissociation, demonstrating abnormal global level processing under all conditions, whereas RPD patients showed abnormal local level processing mainly when attention was biased toward the local level. These findings link side of motor symptom onset to visuospatial cognitive abilities that depend upon the contralateral TP, highlighting that side of onset can predict visuospatial impairments, and provide evidence that an inferior parietal-basal ganglia pathway involving the caudate head and the hemispherically asymmetrical TP region is necessary for hierarchical pattern perception. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parallel and competitive processes in hierarchical analysis: Perceptual grouping and encoding of closure.

The role of perceptual grouping and the encoding of closure of local elements in the processing of hierarchical patterns was studied. Experiments 1 and 2 showed a global advantage over the local level for 2 tasks involving the discrimination of orientation and closure, but there was a local advantage for the closure discrimination task relative to the orientation discrimination task. Experiment 3 showed a local precedence effect for the closure discrimination task when local element grouping was weakened by embedding the stimuli from Experiment 1 in a background made up of cross patterns. Experiments 4A and 4B found that dissimilarity of closure between the local elements of hierarchical stimuli and the background figures could facilitate the grouping of closed local elements and enhanced the perception of global structure. Experiment 5 showed that the advantage for detecting the closure of local elements in hierarchical analysis also held under divided- and selective-attention conditions. Results are consistent with the idea that grouping between local elements takes place in parallel and competes with the computation of closure of local elements in determining the selection between global and local levels of hierarchical patterns for response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Radioligand-binding assay employing P-glycoprotein-overexpressing cells: testing drug affinities to the secretory intestinal multidrug transporter

We report a perceptual phenomenon that originates from a nonlinear operation during the visual process, and we use these observations to study the functional organization of the responsible nonlinearity; the regulation of visual sensitivity to light. When the contrast of a high frequency grating was modulated while its spatial and temporal average luminance was kept constant, observers saw brightness changes or desaturation in the field. If the contrast was modulated periodically between zero and a peak value, observers saw vivid flicker (contrast-modulation flicker), and this flicker could be seen even when the grating was too fine to be visually resolved as a pattern. This uniform-field flicker can be nulled by a modulation of space-average luminance at the contrast-modulation frequency, with appropriate phase and modulation depth. Contrast-modulation flicker is still measurable with gratings at 100 cycles/deg. The dynamics of contrast-modulation flicker suggest that it results from an early sensitivity-controlling mechanism, acting very rapidly (within about 20 msec). Its dependence on stimulus spatial frequency implies a strictly local luminance nonlinearity, one that either resides within individual photoreceptors or operates on signals from individual receptors.     

Hemispheric and attentional contributions to perceptual organization deficits on the global-local task in schizophrenia.

Right and left hemisphere hypotheses have been proposed to account for cognitive deficits in schizophrenia. To examine these hypotheses, perception of global-local patterns was studied in 22 patients with schizophrenia and 28 normal comparison participants. The patients with schizophrenia showed an abnormally exaggerated global processing advantage when attention was divided between global and local levels but not when participants were instructed to attend to either the local or global level. This finding suggested a local processing (left hemisphere) deficit, which was overcome through strategic attentional allocation (instructional set). When the stimulus visual angle was reduced from 9° to 3°, the normal participants showed a shift from a local to a global processing advantage, but the patients did not. This finding suggested a more subtle deficit in strategic attentional processes that develop through exposure to stimulus context. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The importance of information localization in scene gist recognition.

People can recognize the meaning or gist of a scene from a single glance, and a few recent studies have begun to examine the sorts of information that contribute to scene gist recognition. The authors of the present study used visual masking coupled with image manipulations (randomizing phase while maintaining the Fourier amplitude spectrum; random image structure evolution [RISE]; J. Sadr & P. Sinha, 2004) to explore whether and when unlocalized Fourier amplitude information contributes to gist perception. In 4 experiments, the authors found that differences between scene categories in the Fourier amplitude spectrum are insufficient for gist recognition or gist masking. Whereas the global 1/f spatial frequency amplitude spectra of scenes plays a role in gist masking, local phase information is necessary for gist recognition and for the strongest gist masking. Moreover, the ability to recognize the gist of a target image was influenced by mask recognizability, suggesting that conceptual masking occurs even at the earliest stages of scene processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)