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At least 19 recordsLinked to original sources
PubMed2002

The role of contrast polarity in perceptual closure.

Perceptual closure is one of the principles by which the visual system groups disjointed contour segments belonging to a single object. Recently it has been reported that grouping based on perceptual closure operates only upon contour elements of a consistent contrast sign and is eliminated when closed contours contain contrast reversing segments [Elder, J. & Zucker, S. (1994) A measure of closure. Vision Research, 22, 3361-3369]. The present study re-examines the effect of contrast polarity reversals on perceptual closure with special emphasis on differentiating the effect of the presence of contrast polarity reversals from the effect of their placement along the bounding contour. Results show that perceptual closure exhibits a strong dependence on the distribution of contrast polarity reversals: closed configurations containing intra-figural contrast reversals can be processed rapidly when contrast sign does not change at the corners of two-dimensional shapes.

Adult↗
PubMed1998

On the generality of the perceptual closure effect.

Perceptual closure is a process whereby an incomplete stimulus is perceived to be complete. J. G. Snodgrass and K. Feenan (1990) argued that perceptual closure during a study episode is an important factor in producing large priming effects in picture fragment identification. They found that a moderately fragmented study picture produced more priming than either a very fragmented or an intact study picture and argued that this inverted U-shaped function is a signature of the perceptual closure effect. The experiments in this study, extend these results to word fragment identification by showing that (a) the most effective prime, for both unspeeded and speeded word fragment identification is a moderately fragmented study word; (b) the sharpness of the U-shaped gradient is the same whether the perceptual feedback during study is a word (in a font different from that of the fragmented study word) or a picture; and (c) although a fragmented study picture primes subsequent word fragment identification, it does not produce the inverted U-shaped function, thereby showing that perceptual closure reflects perceptual rather than conceptual priming.

Adult↗
PubMed1990

Priming effects in picture fragment completion: support for the perceptual closure hypothesis.

The perceptual closure hypothesis says that priming will be optimum when just enough information is available in the prime to support closure. Across 5 experiments, a moderately complete fragmented image (Level 4) produced more priming than an almost complete (Level 7) or a very incomplete (Level 1) fragmented image. Only Level 4 priming was improved by increases in prime duration and by showing the prime again after Ss attempted to identify it. Explicit memory played little role in primed fragment completion except for Level 1 priming, in which specific fragment memory was responsible for the entire effect. In contrast, true perceptual learning was shown to be responsible for Level 4 and Level 7 priming. These priming effects cannot be accounted for by the transfer-appropriate procedures approach of Roediger and his colleagues because Level 1 priming produced less transfer to Level 1 identification at test than Level 4 priming did.

Adult↗
PubMed1995

Lateralization of perceptual closure ability.

The present study investigated lateralization of perceptual closure ability. A zero-power, partially occluded, soft contact-lens system was used to lateralize visual input. This technique has been shown to create reliable artificial visual-field deficits when used in situations offering unlimited duration of stimulus exposure. The Street Gestalt Completion Test was administered to 18 right-handed men with no history of head trauma, neurological disorders, or familial sinistrality. Using repeated-measures analyses, and controlling for age, we found no significant hemispheric advantage for either speed or accuracy of performance.

Adolescent↗
PubMed2000

Activation timecourse of ventral visual stream object-recognition areas: high density electrical mapping of perceptual closure processes.

Object recognition is achieved even in circumstances when only partial information is available to the observer. Perceptual closure processes are essential in enabling such recognitions to occur. We presented successively less fragmented images while recording high-density event-related potentials (ERPs), which permitted us to monitor brain activity during the perceptual closure processes leading up to object recognition. We reveal a bilateral ERP component (N(cl)) that tracks these processes (onsets approximately 230 msec, maximal at approximately 290 msec). Scalp-current density mapping of the N(cl) revealed bilateral occipito-temporal scalp foci, which are consistent with generators in the human ventral visual stream, and specifically the lateral-occipital or LO complex as defined by hemodynamic studies of object recognition.

Adolescent↗
PubMed1988

Effects of aging on perceptual closure.

Two research strategies were employed to investigate reasons for the poorer performance associated with increased age on perceptual closure tasks involving the integration and identification of incomplete pictures. One strategy consisted of examining age differences in measures designed to reflect the proficiency of processing components presumed to be involved in the closure task. The performance of older adults was significantly worse than that of young adults on each measure, suggesting that the age differences in the criterion task could not be localized in a single specific component. The second strategy involved determining whether young and old adults differed in the effects of practice or in the amount of specific and general transfer resulting from that practice. No age differences other than those in the overall level of performance were discovered, indicating that the age-associated problem may be independent of the processes contributing to the acquisition and transfer of new information. It was suggested that the age differences in perceptual closure tasks originate because of a general inefficiency in information processing due to a reduction in some type of general-purpose processing resource, and not because of a limitation in a single specific process.

Adolescent↗
PubMed2005

Menstrual cycle effects on perceptual closure mediate changes in performance on a fragmented objects test of implicit memory.

Healthy premenopausal women with regular menstrual cycles were assessed on a fragmented objects test of implicit memory. Testing took place at either the low estrogen (n=17) or the high estrogen (n=16) stages of the menstrual cycle. Concentrations of ovarian hormones were confirmed by saliva assays. Both groups of women exhibited a priming effect, in that primed objects were identified faster and at greater fragmentation than unprimed objects. There was no evidence that high estrogen inhibits perceptual object priming. However, women at the menstrual phase were able to identify both primed and unprimed objects at a more degraded level of fragmentation. Changes in perceptual closure over the menstrual cycle may be the basis for the changes in performance on the fragmented objects test observed in previous studies.

Adult↗
PubMed1992

Perceptual closure and object identification: electrophysiological responses to incomplete pictures.

Event-related potentials were recorded during the naming of pictures of concrete objects. The pictures were presented at three levels of completeness: 10, 30, and 60%. The ERP waveforms were evaluated according to the level of picture completeness and the correctness of naming. A negative wave in the latency range of 250-550 ms was significantly more negative when the pictures were more incomplete, regardless of the correctness of response. This N400 wave is proposed as being related to hypotheses about the identity of the object. A late positive wave in the latency range of 550-650 ms followed the negativity, but only when the response was correct. This may reflect the subject's certainty about the perceptual analysis, a verification of the identity of the object. A slow parietal negativity lasting up to 2 sec was largest for the least complete picture. This therefore varied with the perceptual difficulty.

Adult↗
PubMed2002

Impaired visual object recognition and dorsal/ventral stream interaction in schizophrenia.

BACKGROUND: Schizophrenia is associated with well-documented deficits in high-order cognitive processes such as attention and executive functioning. The integrity of sensory-level processing, however, has been evaluated only to a limited degree. Our study evaluated the ability of patients with schizophrenia to recognize complete objects based on fragmentary information, a process termed perceptual closure. Perceptual closure processes are indexed by closure negativity (N(cl)), a recently defined event-related potential (ERP) component that is generated within the visual association cortex. This study assessed the neural integrity of perceptual closure processes in schizophrenia by examining N(cl) generation. Generation of the preceding positive (P1) and negative (N1) ERP components was also examined. METHODS: We evaluated 16 patients with chronic schizophrenia and 16 healthy comparison subjects. Successively less fragmented images were presented during high-density ERP recording, which permitted the monitoring of brain activity during perceptual closure processes prior to object recognition. Analyses were performed at parieto-occipital and occipitotemporal sites consistent with dorsal and ventral stream generators of P1, N1, and N(cl). RESULTS: Patients with schizophrenia showed significant impairment in the ability to recognize fragmented objects, along with impaired generation of N(cl). The amplitude of visual P1 was significantly reduced, particularly over dorsal stream sites. In contrast, the generation of visual N1 was intact. CONCLUSIONS: Patients with schizophrenia are profoundly impaired in perceptual closure as indicated by both impaired performance and impaired N(cl) generation. The selective impairment in dorsal stream P1 is consistent with prior reports of impaired magnocellular processing in schizophrenia. By contrast, intact ventral N1 generation suggests that the initial stages of ventral stream processing are relatively preserved and that impaired magnocellular dorsal stream functioning in schizophrenia may lead to secondary dysregulation of ventral stream object recognition processing.

Adult↗
PubMed2005

Spatiotemporal dynamics of human object recognition processing: an integrated high-density electrical mapping and functional imaging study of "closure" processes.

Humans are capable of recognizing objects, often despite highly adverse viewing conditions (e.g., occlusion). The term "perceptual closure" has been used to refer to the neural processes responsible for "filling-in" missing information in the visual image under such conditions. Closure phenomena have been linked to a group of object recognition areas, the so-called lateral-occipital complex (LOC). Here, we investigated the spatiotemporal dynamics of perceptual closure processes by coregistering data from high-density electrical recordings (ERPs) and functional magnetic resonance imaging (fMRI) while subjects participated in a perceptual closure task. Subjects were presented with highly fragmented images and control scrambled images. Fragmented images were calibrated to be 'just' recognizable as objects (that is, perceptual closure was necessary), whereas the scrambled images were unrecognizable. Comparison of responses to these two stimulus classes revealed the neural processes underlying perceptual closure. fMRI revealed an object recognition system that mediates these closure processes, the core of which consists of the LOC regions. ERP recordings resulted in the well-characterized N(CL) component (for negativity associated with closure), a robust relative negativity over bilateral occipito-temporal scalp that occurs in the 230-400 ms timeframe. Our investigations further revealed an extended network of dorsal and frontal regions, also involved in perceptual closure processes. Inverse source analysis showed that the major generators of N(CL) localized to the identical regions within LOC revealed by the fMRI recordings and detailed the temporal dynamics across these LOC regions including interactions between LOC and these other nodes of the object recognition circuit.

Adult↗
PubMed2001

Impaired sensory processing as a basis for object-recognition deficits in schizophrenia.

OBJECTIVE: Individuals are able to recognize common objects even when portions of them are obscured from view, reflecting the operation of neural perceptual closure processes. This study evaluates the integrity of object recognition and perceptual closure as a function of sensory and cognitive manipulations. METHOD: Object recognition was examined in 26 subjects with schizophrenia and 23 nonpsychiatric comparison subjects of similar age with a presentation of fragmented pictures by means of the ascending method of limits. The effects of prior exposure to subsets of stimuli and of word prompting were examined in separate testing phases. Demographic and clinical characteristics were evaluated as covariates. RESULTS: Although they had impairments in perceptual closure, schizophrenic patients showed improvement in performance equivalent to that of nonpatient comparison subjects with prior exposure to the pictures (i.e., repetition priming) and with presentation of valid word prompts. A significant correlation was found between impaired performance and the severity of negative symptoms. CONCLUSIONS: The results support models of widespread dysfunction in information processing in patients with schizophrenia involving both sensory and cognitive regions. Perceptual closure is significantly impaired in schizophrenic patients; however, this deficit in sensory precision is dissociated from the effects of higher-order repetition priming and word prompting. Furthermore, this work suggests that deficits in perceptual closure may contribute to the muted world experience of patients with the persistent negative symptoms of schizophrenia.

Adult↗