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)     

Separability and integrality of global and local levels of hierarchical patterns.

Used a constrained classification task to examine the perceptual relations between global and local levels in hierarchical patterns composed of many, relatively small elements and those composed of few, relatively large elements. In 4 experiments, 52 18–35 yr olds made classifications based on form or texture or according to the shape of the configuration or the elements. Results indicate that configural and elemental levels were perceptually separable for many-element patterns when processed as form and texture. Ss could attend to either level without being affected by variation along the irrelevant dimension. However, when the same many-element patterns were processed for global and local shape. Ss could not selectively attend to either level. For few-element patterns, global configuration and local elements appeared to be perceptually integral dimensions. Results are discussed in terms of the global precedence hypothesis and explanations of integral and separable dimensions. (28 ref) (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)     

Faces are "spatial"--holistic face perception is supported by low spatial frequencies.

Faces are perceived holistically, a phenomenon best illustrated when the processing of a face feature is affected by the other features. Here, the authors tested the hypothesis that the holistic perception of a face mainly relies on its low spatial frequencies. Holistic face perception was tested in two classical paradigms: the whole-part advantage (Experiment 1) and the composite face effect (Experiments 2-4). Holistic effects were equally large or larger for low-pass filtered faces as compared to full-spectrum faces and significantly larger than for high-pass filtered faces. The disproportionate composite effect found for low-pass filtered faces was not observed when holistic perception was disrupted by inversion (Experiment 3). Experiment 4 showed that the composite face effect was enhanced only for low spatial frequencies, but not for intermediate spatial frequencies known be critical for face recognition. These findings indicate that holistic face perception is largely supported by low spatial frequencies. They also suggest that holistic processing precedes the analysis of local features during face perception. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Uniform connectedness and grouping in the perceptual organization of hierarchical patterns

The principle of uniform connectedness (S. E. Palmer & I. Rock, 1994) states that connected regions of uniform visual properties correspond to the entry-level units of visual stimuli. The implications of this principle for the perceptual organization of hierarchical patterns were investigated in 3 experiments. Primed matching and visual search were used to examine the microgenesis of organization for patterns that vary in number and relative size of their elements. Results for the few-element patterns showed an initial representation of elements with a weaker representation of global configuration. Grouping of elements into global configuration consolidated with time and involved focused attention. The entry-level units of many-element patterns were global configuration and texture. Individuation of elements occurred later and involved focused attention. These findings are discussed with reference to processes underlying perceptual organization.     

Phonetic category structure of [I]: extent, best exemplars, and organization

The current investigation examined the structure of the phonetic category [I] for 13 listeners. Experiments reported are results from identification, "best exemplar," and discrimination tasks using 105 [I] stimuli. The tokens were synthesized long a mel-spaced vowel continuum that differed in first and second formants. All stimuli ended in a 30 ms [b] sound. Results showed that 10 of 13 listeners demonstrated differing choices of the best exemplars, although most were within 37.5 mels of the central best exemplar chosen in the first experiment. Seven of the participants demonstrated "circular" patterns in identification of the [I] category that appeared to be organized around a central "best exemplar." Six participants showed other identification patterns: "downward," "upward," and "left-extending," with "best exemplars" on an edge or border of the phonetic categories. Graded category structure from a central "best exemplar" was apparent only in the averaged identification results, and not for individual participants. The size of the [I] category was significantly smaller than that surrounding the [i] best exemplar reported in a prior study by Sussman and Lauckner-Morano (1995). Finally, listeners had equivalent or better discrimination sensitivity with the best exemplar as the fixed standard compared to that for a "poor" exemplar token 45 mels away from the best exemplar. Results showed that phonetic category structure for the lax vowel [I] was different from the similar, but tense vowel [i]. The findings question whether prototype theory is generalizable to vowel categories other than [i].     

Visual response properties of striate cortical neurons projecting to area MT in macaque monkeys

We have previously shown that some neurons in extrastriate area MT are capable of signaling the global motion of complex patterns; neurons randomly sampled from V1, on the other hand, respond only to the motion of individual oriented components. Because only a small fraction of V1 neurons projects to MT, we wished to establish the processing hierarchy more precisely by studying the properties of those neurons projecting to MT, identified by antidromic responses to electrical stimulation of MT. The neurons that project from V1 to MT were directionally selective and, like other V1 neurons, responded only to the motion of the components of complex patterns. The projection neurons were predominantly "special complex," responsive to a broad range of spatial and temporal frequencies, and sensitive to very low stimulus contrasts. The projection neurons thus comprise a homogeneous and highly specialized subset of V1 neurons, consistent with the notion that V1 acts as clearing house of basic visual measurements, distributing information appropriately to higher cortical areas for specialized analysis.     

Detection and recognition of radial frequency patterns

Detection thresholds for radial deformations of circular contours were measured using a range of radii and contour peak spatial frequencies. For radial frequencies above two cycles, thresholds were found to be a constant fraction of the mean radius across a four-octave range of pattern radii and peak spatial frequencies (mean Weber fraction: 0.003-0.004). At low radial frequencies, thresholds were unaffected by contrast reduction. In 167 ms presentations, subjects were able to identify radial frequencies of six cycles and below with an accuracy of over 90% correct even when phase was randomized. The extreme sensitivity of subjects to these radial deformations (as low as 2-4 s of arc) cannot be explained by local orientation or curvature analysis, and points instead to the global pooling of contour information at intermediate levels of form vision.     

Hemispheric asymmetry for visual information processing

The left and right hemispheres of humans do not handle all aspects of visual information processing with equal ability. This is illustrated by a review of research concerning the processing of global versus local stimulus properties, low versus high spatial frequencies, and coordinate versus categorical spatial relationships. In general, the right hemisphere is dominant for processing global aspects of visual stimuli that are carried by low spatial frequencies, for the processing of coordinate spatial relationships and, perhaps, for extracting information from the magnocellular visual pathway. In something of a complementary manner, the left hemisphere is dominant for processing local aspects of visual stimuli that are carried by high spatial frequencies and, perhaps, for processing categorical spatial relationships and for extracting information from parvocellular visual pathway. Consideration is given to developmental mechanisms that may underlie the emergence of hemispheric asymmetry for these interrelated aspects of visual information processing.     

Anticipating by Pigeons Depends on Local Statistical Information in a Serial Response Time Task.

Pigeons responded in a serial response time task patterned after that of M. J. Nissen and P. Bullemer (1987) with humans. Experiment 1 produced global facilitation: Response times in repeating lists of locations were faster than when locations were random. Response time to a spatial location was also a function of both that location's 1st- and 2nd-order local predictability, in rough agreement with the Hick-Hyman law, according to which response time is a linear function of amount of information. Experiment 2 showed that both local and global facilitation is limited to moderate response-to-stimulus intervals of about 0.50 to 2.00 s. Experiment 3 showed that response time did not depend on global statistical information. Overall, local and global performances depended on local statistical information, but global performance did not depend on global information. Local facilitation was interpreted in plain English as anticipating. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Transsaccadic representation of layout: What is the time course of boundary extension?

How rapidly does boundary extension occur? Across experiments, trials included a 3-scene sequence (325 ms/picture), masked interval, and repetition of 1 scene. The repetition was the same view or differed (more close-up or wide angle). Observers rated the repetition as same as, closer than, or more wide angle than the original view on a 5-point scale. Masked intervals were 100, 250, 625, or 1,000 ms in Experiment 1 and 42, 100, or 250 ms in Experiments 2 and 3. Boundary extension occurred in all cases: Identical views were rated as too "close-up," and distractor views elicited the rating asymmetry typical of boundary extension (wider angle distractors were rated as being more similar to the original than were closer up distractors). Most important, boundary extension was evident when only a 42-ms mask separated the original and test views. Experiments 1 and 3 included conditions eliciting a gaze shift prior to the rating test; this did not eliminate boundary extension. Results show that boundary extension is available soon enough and is robust enough to play an on-line role in view integration, perhaps supporting incorporation of views within a larger spatial framework. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

How Different Spatial-Frequency Components Contribute to Visual Information Acquisition.

We test 3 theories of global and local scene information acquisition, defining global and local in terms of spatial frequencies. By independence theories, high- and low-spatial-frequency information are acquired over the same time course and combine additively. By global-precedence theories, global information acquisition precedes local information acquisition, but they combine additively. By interactive theories, global information also affects local-information acquisition rate. We report 2 digit-recall experiments. In the 1st, we confirmed independence theories. In the 2nd, we disconfirmed both independence theories and interactive theories, leaving global-precedence theories as the remaining alternative. We show that a specific global-precedence theory quantitatively accounted for Experiments 1-2 data as well as for past data. We discuss how their spatial-frequency definition of spatial scale comports with definitions used by others, and we consider the suggestion by P. G. Schyns and colleagues (e.g., D. J. Morrison & Schyns, 2001) that the visual system may act flexibly rather than rigidly in its use of spatial scales. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fibroblasts prevent apoptosis of IL-2-deprived T cells without inducing proliferation: a selective effect on Bcl-XL expression

Tumour hypoxia is well recognised as a major factor contributing to radioresistance. This article examines the role of hypoxia in influencing the treatment outcome following radiotherapy (RT), and reviews the rationale and results of clinical trials that utilise hypoxic sensitizers or cytotoxins in the treatment of head and neck carcinoma. Histologic evidence for tumour hypoxia in human neoplasms was first reported in 1955. Since then, direct measurement by microelectrodes has revealed heterogeneity in intratumoural oxygen concentrations, and low oxygen concentrations are associated with poor local-regional control by RT. These findings coupled with the result of nuclear imaging studies employing radiolabelled imidazoles, provide strong evidence for the existence of tumour hypoxia which influences RT treatment outcome. Hyperbaric oxygen (HBO) trials for head and neck cancer, conducted in the early 1970s, demonstrated that HBO improved local control and survival rates in patients with head and neck cancer receiving radiotherapy (RT). Since the mid-1970s, clinical research in overcoming tumour hypoxia was mainly centred on the use of nitro-imidazoles as hypoxic cell sensitizers. However, the results from several major clinical trials remain inconclusive. Specifically, the Radiation Therapy Oncology Group (RTOG) misonidazole head and neck trial (298 patients) showed no benefit. The Danish misonidazole trial (626 patients) showed no overall benefit, however positive results were observed in a subgroup (304 pharyngeal cancer patients). Although the European Organisation for Research and Teaching of Cancer (EORTC) misonidazole trial with hyperfractionated RT showed no benefit, the Danish nimorazole trial demonstrated an overall benefit in survival as well as local control. The European etanidazole (ETA) trial (374 patients) showed no advantage of adding the drug to RT. The RTOG ETA trial (504 patients) showed no global benefit. However, positive results were observed in a subset of patients with early nodal disease (197 patients). In addition, a recent meta-analysis by Overgaard, utilising pooled results in the literature demonstrated that modification of tumour hypoxia significantly improved local-regional control in head and neck cancers with an odds ratio of 1.23 (95% confidence limits 1.09 to 1.37). Hypoxic cytotoxins, such as tirapazamine, represent a novel approach in overcoming radioresistant hypoxic cells. Tirapazamine is a bioreductive agent which, by undergoing one electron reduction in hypoxic conditions, forms cytotoxic free radicals that produce DNA strand breaks causing cell death. In vitro and in vivo laboratory studies demonstrate that tirapazamine is 40 to 150 times more toxic to cells under hypoxic conditions as compared to oxygenated conditions and that tirapazamine is superior to ETA in enhancing fractionated irradiation in mouse SCCVII and other tumour types with an enhancement ratio of 1.5 to 3.0. Phase I studies demonstrated that therapeutic doses of tirapazamine can be given safely. A multi-institutional phase II trial using tirapazamine with concurrent RT for head and neck cancer is now in progress.     

Mechanisms of spatial impairment in Alzheimer's disease subgroups: Differential breakdown of directed attention to global-local stimuli.

Global–local stimuli (e.g., a large 1 composed of small 2s) were presented to subgroups of patients with Alzheimer's disease (AD) and to normal controls in a directed-attention reaction time (RT) experiment. Pronounced dissociations in performance were found among the AD subgroups. Those patients who displayed greater impairment in verbal than in spatial skills on traditional clinical tests had particular difficulty processing local (detail) forms, whereas patients who had greater spatial than verbal impairment exhibited striking deficits in processing global (configural) forms. Results indicate that the AD patients were impaired primarily in inhibiting responses associated with their strong area when attending to forms in their weak area, although they did evince mild impairment in the perceptual processing of forms in their weak area as well. Thus, it appears that the AD patients' global–local processing deficits interacted with deficient inhibitory mechanisms to produce their patterns of deficits on the directed attention task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Emotion perception is mediated by spatial frequency content.

Spatial frequencies have been shown to play an important role in face identification, but very few studies have investigated the role of spatial frequency content in identifying different emotions. In the present study we investigated the role of spatial frequency in identifying happy and sad facial expressions. Two experiments were conducted to investigate (a) the role of specific spatial frequency content in emotion identification, and (b) hemispherical asymmetry in emotion identification. Given the links between global processing, happy emotions, and low frequencies, we hypothesized that low spatial frequencies would be important for identifying the happy expression. Correspondingly, we also hypothesized that high spatial frequencies would be important in identifying the sad expression given the links between local processing, sad emotions, and high spatial frequencies. As expected we found that the identification of happy expression was dependent on low spatial frequencies and the identification of sad expression was dependent on high spatial frequencies. There was a hemispheric asymmetry with the identification of sad expression, especially in the right hemisphere, possibly mediated by high spatial frequency content. Results indicate the importance of spatial frequency content in the identification of happy and sad emotional expressions and point to the mechanisms involved in emotion identification. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

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)     

What's "up" with God? Vertical space as a representation of the divine.

"God" and "Devil" are abstract concepts often linked to vertical metaphors (e.g., "glory to God in the highest," "the Devil lives down in hell"). It is unknown, however, whether these metaphors simply aid communication or implicate a deeper mode of concept representation. In 6 experiments, the authors examined the extent to which the vertical dimension is used in noncommunication contexts involving God and the Devil. Experiment 1 established that people have implicit associations between God-Devil and up-down. Experiment 2 revealed that people encode God-related concepts faster if presented in a high (vs. low) vertical position. Experiment 3 found that people's memory for the vertical location of God- and Devil-like images showed a metaphor-consistent bias (up for God; down for Devil). Experiments 4, 5a, and 5b revealed that people rated strangers as more likely to believe in God when their images appeared in a high versus low vertical position, and this effect was independent of inferences related to power and likability. These robust results reveal that vertical perceptions are invoked when people access divinity-related cognitions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Local and relational aspects of face distinctiveness

Distinctiveness contributes strongly to the recognition and rejection of faces in memory tasks. In four experiments we examine the role played by local and relational information in the distinctiveness of upright and inverted faces. In all experiments subjects saw one of three versions of a face: original faces, which had been rated as average in distinctiveness in a previous study (Hancock, Burton, & Bruce, 1996), a more distinctive version in which local features had been changed (D-local), and a more distinctive version in which relational features had been changed (D-rel). An increase in distinctiveness was found for D-local and D-rel faces in Experiment 1 (complete faces) and 3 and 4 (face internals only) when the faces had to be rated in upright presentation, but the distinctiveness of the D-rel faces was reduced much more than that of the D-local versions when the ratings were given to the faces presented upside-down (Experiments 1 and 3). Recognition performance showed a similar pattern: presented upright, both D-local and D-rel revealed higher performance compared to the originals, but in upside-down presentation the D-local versions showed a much stronger distinctiveness advantage. When only internal features of faces were used (Experiments 3 and 4), the D-rel faces lost their advantage over the Original versions in inverted presentation. The results suggest that at least two dimensions of facial information contribute to a face's apparent distinctiveness, but that these sources of information are differentially affected by turning the face upside-down. These findings are in accordance with a face processing model in which face inversion effects occur because a specific type of information processing is disrupted, rather than because of a general disruption of performance.     

Two dissociable updating processes in working memory.

The authors show that the updating of working memory (WM) representations is carried out by the cooperative act of 2 dissociable reaction time (RT) components: a global updating process that provides stability by shielding WM contents against interference and a local process that provides flexibility. Participants kept track of 1?3 items (digits or Gibson figures). In each trial, the items either were similar to those in the previous trial or were different in any or all of the items. Experiments 1 and 2 established the existence of 2 independent RT components representing the 2 updating processes. Global updating cost was sensitive to total number of items in WM (set size), regardless of the number of items that actually were modified. Local updating cost was sensitive to the number of modified items, regardless of the set size. Experiment 3 showed that participants had to dismantle the representation formed by previous global updating in order to carry out new updating. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rotation of mental images and asymmetries in word recognition in disabled readers.

Two experiments with 72 right-handed children (9–11 yrs old) revealed marked dissimilarities in perceptual coding between impaired and fluent readers. In Exp I, 26 boys with reading disabilities and average intelligence were compared to 26 good readers on a test of visual–spatial, short-term memory. Both groups performed equally well in their spatial recall on transformed visual fields. However, poor readers coded the test stimuli differently, in a nonanalytic and synchronous fashion. In a follow-up experiment, 10 disabled readers compared with 10 good readers showed a lower right- over left-field advantage when reporting single words presented tachistoscopically. Taken together, results disconfirm the widely held ideas that poor readers are suffering from spatial disorientation, left–right confusion, mirror-image equivalence, or lack of cerebral dominance. Findings suggest that the perceptual "anormalies" often linked with reading disability may result from nonpathological variations in the structural operations used to encode visual information. This difference in the organization of encodings in visual memory may be related to asymmetries in brain functioning. (42 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)