On the generality of the perceptual closure effect

Multimodal Computational Modeling of Visual Object Recognition Deficits but Intact Repetition Priming in Schizophrenia

The term perceptual closure refers to the neural processes responsible for "filling-in" missing information in the visual image under highly adverse viewing conditions such as fog or camouflage. Here we used a closure task that required the participants to identify barely recognizable fragmented line-drawings of common objects. Patients with schizophrenia have been shown to perform poorly on this task. Following priming, controls and importantly patients can complete the line-drawings at greater levels of fragmentation behaviorally, suggesting an improvement in their ability to perform the task. Closure phenomena have been shown to involve a distributed network of cortical regions, notably the lateral occipital complex (LOC) of the ventral visual stream, dorsal visual stream (DS), hippocampal formation (HIPP) and the prefrontal cortex (PFC). We have previously demonstrated the failure of closure processes in schizophrenia and shown that the dysregulation in the sensory information transmitted to the prefrontal cortex plays a critical role in this failure. Here, using a multimodal imaging approach in patients, combining event related electrophysiological recordings (ERP) and functional magnetic resonance imaging (fMRI), we characterize the spatiotemporal dynamics of priming in perceptual closure. Using directed functional connectivity measures we demonstrate that priming modifies the network-level interactions between the nodes of closure processing in a manner that is functionally advantageous to patients resulting in the mitigation of their deficit in perceptual closure.

Integration of Partial Information Within and Across Modalities: Contributions to Spoken and Written Sentence Recognition

PURPOSE

This study evaluated the extent to which partial spoken or written information facilitates sentence recognition under degraded unimodal and multimodal conditions.

METHOD

Twenty young adults with typical hearing completed sentence recognition tasks in unimodal and multimodal conditions across 3 proportions of preservation. In the unimodal condition, performance was examined when only interrupted text or interrupted speech stimuli were available. In the multimodal condition, performance was examined when both interrupted text and interrupted speech stimuli were concurrently presented. Sentence recognition scores were obtained from simultaneous and delayed response conditions.

RESULTS

Significantly better performance was obtained for unimodal speech-only compared with text-only conditions across all proportions preserved. The multimodal condition revealed better performance when responses were delayed. During simultaneous responses, participants received equal benefit from speech information when the text was moderately and significantly degraded. The benefit from text in degraded auditory environments occurred only when speech was highly degraded.

CONCLUSIONS

The speech signal, compared with text, is robust against degradation likely due to its continuous, versus discrete, features. Allowing time for offline linguistic processing is beneficial for the recognition of partial sensory information in unimodal and multimodal conditions. Despite the perceptual differences between the 2 modalities, the results highlight the utility of multimodal speech + text signals.

On the role of the upper part of words in lexical access: evidence with masked priming

More than 100 years ago, Huey (1908/1968) indicated that the upper part of words was more relevant for perception than the lower part. Here we examined whether mutilated words, in their upper/lower portions (e.g., ), can automatically access their word units in the mental lexicon. To that end, we conducted four masked repetition priming experiments with the lexical decision task. Results showed that mutilated primes produced a sizeable masked repetition priming effect. Furthermore, the magnitude of the masked repetition priming effect was greater when the upper part of the primes was preserved than when the lower portion was preserved-this was the case not only when the mutilated words were presented in lower case but also when the mutilated words were presented in upper case. Taken together, these findings suggest that the front-end of computational models of visual-word recognition should be modified to provide a more realistic account at the level of letter features.

Auditory and nonauditory factors affecting speech reception in noise by older listeners

Speech reception thresholds (SRTs) for sentences were determined in stationary and modulated background noise for two age-matched groups of normal-hearing (N = 13) and hearing-impaired listeners (N = 21). Correlations were studied between the SRT in noise and measures of auditory and nonauditory performance, after which stepwise regression analyses were performed within both groups separately. Auditory measures included the pure-tone audiogram and tests of spectral and temporal acuity. Nonauditory factors were assessed by measuring the text reception threshold (TRT), a visual analogue of the SRT, in which partially masked sentences were adaptively presented. Results indicate that, for the normal-hearing group, the variance in speech reception is mainly associated with nonauditory factors, both in stationary and in modulated noise. For the hearing-impaired group, speech reception in stationary noise is mainly related to the audiogram, even when audibility effects are accounted for. In modulated noise, both auditory (temporal acuity) and nonauditory factors (TRT) contribute to explaining interindividual differences in speech reception. Age was not a significant factor in the results. It is concluded that, under some conditions, nonauditory factors are relevant for the perception of speech in noise. Further evaluation of nonauditory factors might enable adapting the expectations from auditory rehabilitation in clinical settings.

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.

Adapting a memory framework (source monitoring) to the study of closure processes

The present experiments adapt a memory framework (source monitoring) to the study of closure processes. Closure processes are invoked as explanatory mechanisms underlying the ability to identify objects under conditions of incomplete visual information. If closure processes are activated, filling in missing pieces of visual information, intriguing memory predictions follow. When making source judgments about the way in which visual information was experienced initially (e.g., complete or incomplete in form), a particular kind of memory error should be evident. Incomplete visual information should be remembered as complete in form, and indeed, this error is observed. The present experiments test alternative interpretations for the initial reports of this memory error in the context of a search task modeled after the Where's Waldo? children's books. The effects of several new factors (e.g., familiarity) are reported, and alternative interpretations for the bias to report complete are eliminated. Findings, therefore, have implications for understanding the mechanisms of closure processes, as well as for the source-monitoring framework itself.

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.