This paper deals with the detection of dim point targets in infrared images. Dim point targets detection is always a difficulty in information processing. Researchers have proposed many effective methods; this paper introduces a new method. Whereas difference method has obtained good result in one dimensional signal processing, this paper manages to apply it to two dimensional signal processing, that is to say, dim point targets detection in infrared images of low SNR. The image background is color noise, and its column correlation is strong. So, ordinary methods probably lose the true targets because of the strong color noise, but unlike them, difference method can overcome this shortcoming, it can eliminate correlation noise and enhance useful information, finally pick out the probable targets from noise background. In the paper, the method was given a more extensive account. In order to improve the detection effect, we utilize prefilter. The prefilter is realized by the alpha filter. Because the same targets have same location in more than three frames, using alpha filter can utilize the information of adjacent frames, increase the SNR of the raw data and reduce the noise of the images.< >
Although neuronal studies have shown that audiovisual integration is regulated by temporal factors, there is still little knowledge about the impact of temporal factors on audiovisual integration in older adults. To clarify how stimulus onset asynchrony (SOA) between auditory and visual stimuli modulates age-related audiovisual integration, 20 younger adults (21-24 years) and 20 older adults (61-80 years) were instructed to perform an auditory or visual stimuli discrimination experiment. The results showed that in younger adults, audiovisual integration was altered from an enhancement (AV, A ± 50 V) to a depression (A ± 150 V). In older adults, the alterative pattern was similar to that for younger adults with the expansion of SOA; however, older adults showed significantly delayed onset for the time-window-of-integration and peak latency in all conditions, which further demonstrated that audiovisual integration was delayed more severely with the expansion of SOA, especially in the peak latency for V-preceded-A conditions in older adults. Our study suggested that audiovisual facilitative integration occurs only within a certain SOA range (e.g., -50 to 50 ms) in both younger and older adults. Moreover, our results confirm that the response for older adults was slowed and provided empirical evidence that integration ability is much more sensitive to the temporal alignment of audiovisual stimuli in older adults.
The basal ganglia, which have been shown to be a significant multisensory hub, are disordered in Parkinson’s disease (PD). This study was to investigate the audiovisual integration of peripheral stimuli in PD patients with/without sleep disturbances. Thirty-six age-matched normal controls (NC) and 30 PD patients were recruited for an auditory/visual discrimination experiment. The mean response times for each participant were analyzed using repeated measures ANOVA and race model. The results showed that the response to all stimuli was significantly delayed for PD compared to NC (allp<0.01). The response to audiovisual stimuli was significantly faster than that to unimodal stimuli in both NC and PD (p<0.001). Additionally, audiovisual integration was absent in PD; however, it did occur in NC. Further analysis showed that there was no significant audiovisual integration in PD with/without cognitive impairment or in PD with/without sleep disturbances. Furthermore, audiovisual facilitation was not associated with Hoehn and Yahr stage, disease duration, or the presence of sleep disturbances (allp>0.05). The current results showed that audiovisual multisensory integration for peripheral stimuli is absent in PD regardless of sleep disturbances and further suggested the abnormal audiovisual integration might be a potential early manifestation of PD.
Studies both on animal and human suggest temporal principle govern audiovisual integration greatly. However, its effect on audiovisual integration of elderly adults remains ambiguous. In this study, unimodal auditory (A), unimodal visual (V) or audiovisual (AV) stimulus with various temporal gap ( 0, 100 or -100 ms) were presented randomly on the left or right hemispace when the subjects attended to both auditory and visual stimuli and were instructed to respond to target stimuli rapidly and accurately. Race modal and SPSS software were used to analyze the data. Our results demonstrated that enhanced audiovisual integration was greatest when auditory and visual stimuli presented simultaneously (P<;0.05); however, when it enlarge to 100 ms, significant enhancement disappeared. Our results confirmed that temporal gaps between visual and auditory stimuli could influence audiovisual interaction in elderly adults under cross-modal attention.
A combination of signals across modalities can facilitate sensory perception. The audiovisual facilitative effect strongly depends on the features of the stimulus. Here, we investigated how sound frequency, which is one of basic features of an auditory signal, modulates audiovisual integration. In this study, the task of the participant was to respond to a visual target stimulus by pressing a key while ignoring auditory stimuli, comprising of tones of different frequencies (0.5, 1, 2.5 and 5 kHz). A significant facilitation of reaction times was obtained following audiovisual stimulation, irrespective of whether the task-irrelevant sounds were low or high frequency. Using event-related potential (ERP), audiovisual integration was found over the occipital area for 0.5 kHz auditory stimuli from 190–210 ms, for 1 kHz stimuli from 170–200 ms, for 2.5 kHz stimuli from 140–200 ms, 5 kHz stimuli from 100–200 ms. These findings suggest that a higher frequency sound signal paired with visual stimuli might be early processed or integrated despite the auditory stimuli being task-irrelevant information. Furthermore, audiovisual integration in late latency (300–340 ms) ERPs with fronto-central topography was found for auditory stimuli of lower frequencies (0.5, 1 and 2.5 kHz). Our results confirmed that audiovisual integration is affected by the frequency of an auditory stimulus. Taken together, the neurophysiological results provide unique insight into how the brain processes a multisensory visual signal and auditory stimuli of different frequencies.
To investigate the neural mechanisms of audiovisual integration in divided attention, we recorded event-related potentials (ERPs) during a divided attention task, in which the stimulus was presented in the auditory (A), visual (V), and in the audiovisual (AV) modalities. ERPs were recorded in normal young subjects, and ERPs elicited by the auditory and visual stimuli when presented alone were summed (`sum' ERP) and compared to the ERP elicited when they were presented simultaneously (`simultaneous' ERP). Two tones (20% white noise and 80% frequent 1000 Hz) and two visual stimuli (20% red white block and 80% black white block) were delivered. Behavioral data and ERPs of AV and (A + V) were analyzed according to different location. Reaction times (RTs) to the stimuli when presented simultaneously were significantly faster than when they were presented alone. Audiovisual integration elicited by stimuli peripherally, which was followed by three more phases of effects that were marked by scalp distribution: (1) the right fronto-central area at 200-220ms after the presentation of the stimulus, (2) centro-medial area at 260-320ms after the presentation of the stimulus, and (3) right posterior area at 340-440ms. We found that these interaction effects occurred slightly later than those reported in previously published AV interaction studies in which AV stimuli were presented centrally.
Although emotional audiovisual integration has been investigated previously, whether emotional audiovisual integration is affected by the spatial allocation of visual attention is currently unknown. To examine this question, a variant of the exogenous spatial cueing paradigm was adopted, in which stimuli varying by facial expressions and nonverbal affective prosody were used to express six basic emotions (happiness, anger, disgust, sadness, fear, surprise) via a visual, an auditory, or an audiovisual modality. The emotional stimuli were preceded by an unpredictive cue that was used to attract participants’ visual attention. The results showed significantly higher accuracy and quicker response times in response to bimodal audiovisual stimuli than to unimodal visual or auditory stimuli for emotional perception under both valid and invalid cue conditions. The auditory facilitation effect was stronger than the visual facilitation effect under exogenous attention for the six emotions tested. Larger auditory enhancement was induced when the target was presented at the expected location than at the unexpected location. For emotional perception, happiness shared the biggest auditory enhancement among all six emotions. However, the influence of exogenous cueing effect on emotional perception seemed to be absent.
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