SEARCH · PubMed Health

Results for “Pattern Recognition, Physiological”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8Linked to original sources

PubMed2006

Spatial representation of neural responses to natural and altered conspecific vocalizations in cat auditory cortex.

This study shows the neural representation of cat vocalizations, natural and altered with respect to carrier and envelope, as well as time-reversed, in four different areas of the auditory cortex. Multiunit activity recorded in primary auditory cortex (AI) of anesthetized cats mainly occurred at onsets (<200-ms latency) and at subsequent major peaks of the vocalization envelope and was significantly inhibited during the stationary course of the stimuli. The first 200 ms of processing appears crucial for discrimination of a vocalization in AI. The dorsal and ventral parts of AI appear to have different roles in coding vocalizations. The dorsal part potentially discriminated carrier-altered meows, whereas the ventral part showed differences primarily in its response to natural and time-reversed meows. In the posterior auditory field, the different temporal response types of neurons, as determined by their poststimulus time histograms, showed discrimination for carrier alterations in the meow. Sustained firing neurons in the posterior ectosylvian gyrus (EP) could discriminate, among others, by neural synchrony, temporal envelope alterations of the meow, and time reversion thereof. These findings suggest an important role of EP in the detection of information conveyed by the alterations of vocalizations. Discrimination of the neural responses to different alterations of vocalizations could be based on either firing rate, type of temporal response, or neural synchrony, suggesting that all these are likely simultaneously used in processing of natural and altered conspecific vocalizations.

Acoustic Stimulation↗

PubMed2006

Representation of object size in the somatosensory system.

In this study we investigate the haptic perception of object size. We report the results from four psychophysical experiments. In the first, we ask subjects to discriminate the size of objects that vary in surface curvature and compliance while changing contact force. We show that objects exhibit size constancy such that perception of object size using haptics does not change with changes in contact force. Based on these results, we hypothesize that size perception depends on the degree of spread between the digits at initial contact with objects. In the second experiment, we test this hypothesis by having subjects continuously contact an object that changes dynamically in size. We show that size perception takes into account the compliance of the object. In the third and fourth experiments we attempt to separate the individual contributions of proprioceptive and cutaneous input. In the third, we test the ability of subjects to perceive object size after altering the sensitivity of cutaneous receptors with adapting vibratory stimuli. The results from this experiment suggest that initial contact is signaled by the cutaneous slowly adapting type 1 afferents (SA1) and/or the rapidly adapting afferents (RA). In the last experiment, we block cutaneous input at the site of contact by anesthetizing the digital nerves and show that proprioceptive information alone provides only a rough estimate of object size. We conclude that the perception of object size depends on inputs from SA1 and possibly RA afferents, combined with inputs from proprioceptive afferents that signal the spread between digits.

Adult↗

PubMed2005

Prevalence of stereotypical responses to mistuned complex tones in the inferior colliculus.

The human auditory system has an exceptional ability to separate competing sounds, but the neural mechanisms that underlie this ability are not understood. Responses of inferior colliculus (IC) neurons to "mistuned" complex tones were measured to investigate possible neural mechanisms for spectral segregation. A mistuned tone is a harmonic complex tone in which the frequency of one component has been changed; that component may be heard as a separate sound source, suggesting that the mistuned tone engages the same mechanisms that contribute to the segregation of natural sounds. In this study, the harmonic tone consisted of eight harmonics of 250 Hz; in the mistuned tone, the frequency of the fourth harmonic was increased by 12% (120 Hz). The mistuned tone elicited a stereotypical discharge pattern, consisting of peaks separated by about 8 ms and a response envelope modulated with a period of 100 ms, which bore little resemblance to the discharge pattern elicited by the harmonic tone or to the stimulus waveform. Similar discharge patterns were elicited from many neurons with a range of characteristic frequencies, especially from neurons that exhibited short-latency sustained responses to pure tones. In contrast, transient and long-latency neurons usually did not exhibit the stereotypical discharge pattern. The discharge pattern was generally stable when the stimulus level or component phase was varied; the major effect of these manipulations was to shift the phase of the response envelope. Simulation of IC responses with a computational model suggested that off-frequency inhibition could produce discharge patterns with these characteristics.

Acoustic Stimulation↗

PubMed2006

Transverse patterning and human amnesia.

The transverse patterning (TP) task (A+ B-, B+ C-, C+ A-) has played a central role in testing the hypothesis that medial-temporal (and, in particular, hippocampal) brain damage selectively impairs learning on at least some classes of configural (i.e., nonlinear) learning tasks. Results in the animal and human literature generally support that hypothesis. Reed and Squire [Impaired transverse patterning in human amnesia is a special case of impaired memory for two-choice discrimination tasks. Behavioral Neuroscience, 113, 3-9, 1999], however, advanced an alternative account in which impaired TP performance in amnesia reflects a generic scaling artifact arising from the greater difficulty of the TP task compared to the elemental (i.e., linear) control task that is typically used. We begin with a critique of Reed and Squire, countering their conceptual arguments and showing that their results, when analyzed appropriately, support the configural deficit hypothesis. We then report results from eight new amnesic patients and controls on an improved version of the TP task. Despite substantial practice, accuracy of patients with bilateral hippocampal damage due to anoxia reached and maintained an asymptote of only 54% correct, well below the maximum accuracy obtainable (67%) in the absence of configural learning. A patient with selective bilateral damage to the anterior thalamic nuclei exhibited a TP accuracy asymptote that was near 67%, a pattern of two out of three correct consecutive trials, and a pattern of nearly always answering correctly for two of the three TP item pairs. These results are consistent with a set of unique and parameter-free predictions of the configural deficit hypothesis.

Aged↗

PubMed2005

Interactive effects of high-pass filtering and masking noise on word recognition.

OBJECTIVES: This study sought to examine the word recognition performance in noise of individuals with a simulated low-frequency hearing loss. The goal was to understand how low-frequency hearing impairment affects performance on tasks that challenge temporal processing skills. METHODS: Twenty-two normal-hearing young adults participated. Monosyllabic words were presented in continuous and interrupted noise at 3 signal-to-noise ratios of -10, 0, and +10 dB. High-pass filtering of the stimuli at 3 different cutoff frequencies (ie, 1,000, 1,250, and 1,500 Hz) simulated the low-frequency hearing impairment. RESULTS: In general, performance decreased with increasing cutoff frequency, was higher for more favorable signal-to-noise ratios, and was superior in the interrupted condition relative to the continuous noise condition. One important revelation was that the magnitude of the performance superiority observed in the interrupted noise condition did not diminish with high-pass filtering; ie, the release from masking in interrupted noise was preserved. CONCLUSIONS: The results of the present study complement previous findings in which this paradigm was used with low-pass filtering to simulate a high-frequency hearing loss. That is to say, low-frequency hearing channels are inherently poorer than high-frequency channels in temporal resolution.

Female↗

PubMed2006

Spinal and brain control of human walking: implications for retraining of walking.

In this update, the authors will discuss evidence for both spinal and brain regulation of walking in humans. They will consider the sensory control of walking in young babies and spinal cord-injured adults, two models with weak descending input from the brain, to suggest that subcortical structures are important in shaping walking behavior. Based on evidence from development, the authors suggest that the primitive pattern of walking seen in babies forms the base upon which additional features are added by supraspinal input as independent walking develops. Increasing evidence suggests the motor cortex is important in the control of level-ground walking in adults, in contrast to quadrupeds. This brain input seems particularly important for distal flexors in the leg. Finally, the authors will consider evidence that the recovery of walking after incomplete spinal cord injuries is dependent on the presence of descending input from the motor cortex and our ability to strengthen that input. These findings imply that training methods for improving walking after injury to the nervous system must promote the involvement of both spinal and brain circuits.

Adult↗

PubMed2004

Attentional influences on functional mapping of speech sounds in human auditory cortex.

BACKGROUND: The speech signal contains both information about phonological features such as place of articulation and non-phonological features such as speaker identity. These are different aspects of the 'what'-processing stream (speaker vs. speech content), and here we show that they can be further segregated as they may occur in parallel but within different neural substrates. Subjects listened to two different vowels, each spoken by two different speakers. During one block, they were asked to identify a given vowel irrespectively of the speaker (phonological categorization), while during the other block the speaker had to be identified irrespectively of the vowel (speaker categorization). Auditory evoked fields were recorded using 148-channel magnetoencephalography (MEG), and magnetic source imaging was obtained for 17 subjects. RESULTS: During phonological categorization, a vowel-dependent difference of N100m source location perpendicular to the main tonotopic gradient replicated previous findings. In speaker categorization, the relative mapping of vowels remained unchanged but sources were shifted towards more posterior and more superior locations. CONCLUSIONS: These results imply that the N100m reflects the extraction of abstract invariants from the speech signal. This part of the processing is accomplished in auditory areas anterior to AI, which are part of the auditory 'what' system. This network seems to include spatially separable modules for identifying the phonological information and for associating it with a particular speaker that are activated in synchrony but within different regions, suggesting that the 'what' processing can be more adequately modeled by a stream of parallel stages. The relative activation of the parallel processing stages can be modulated by attentional or task demands.

Adult↗

PubMed2006

Classification of human breathing sounds by the common vampire bat, Desmodus rotundus.

BACKGROUND: The common vampire bat Desmodus rotundus is one of three bat species that feed exclusively on the blood of mammals often more than 1000 times its size. Vampire bats even feed on human blood. Moreover, they tend to feed on the same individual over consecutive nights. RESULTS: Using psychoacoustical methods, we show that vampire bats can recognize individual humans by their breathing sounds. Accompanying psychoacoustical experiments using the same stimuli and procedure but with human listeners show that even these trained and instructed listeners were unable to achieve the vampire bats' performance under the most difficult conditions, where the breathing sounds had been recorded under physical strain. CONCLUSION: It is suggested that vampire bats can make use of an individual acoustic signature imposed on breathing sounds in a way similar to that in which we identify humans by their vocalizations.

Adult↗

PubMed2004

Reorganization of language-specific cortex in patients with lesions or mesial temporal epilepsy.

OBJECTIVE: To examine brain activation profiles for receptive language function, using magnetoencephalography (MEG), in patients with left hemisphere space-occupying lesions and patients with left temporal lobe epilepsy due to mesial temporal sclerosis (MTS) and to evaluate whether cross- and intrahemispheric plasticity for language varied as a function of lesion type or location. METHODS: Twenty-one patients with MTS and 23 lesional patients underwent preoperative language mapping while performing a word recognition task. The anatomic location of late activity sources was determined by co-registering MEG coordinates onto structural MRI scans. A language laterality index was calculated based on the number of activity sources in each hemisphere. The location of language-specific activity was examined in relation to its proximity or overlap with Wernicke's area. RESULTS: A higher incidence of atypical language lateralization was noted among patients with MTS than lesional patients (43 vs 13%). The majority of MTS patients with early seizure onset (before age 5) showed atypical language lateralization. In contrast, the precise location of receptive language-specific cortex within the dominant hemisphere was found to be atypical (outside of Wernicke's area) in 30% of lesional patients and only 14% of MTS patients. CONCLUSIONS: There is an increased probability of a partial or total displacement of key components of the brain mechanism responsible for receptive language function to the nondominant hemisphere in mesial temporal sclerosis patients. Early onset of seizures is strongly associated with atypical language lateralization. Lesions in the dominant hemisphere tend to result in an intrahemispheric reorganization of linguistic function.

Adolescent↗

PubMed2005

Sensory and motor interhemispheric integration after section of different portions of the anterior corpus callosum in nonepileptic patients.

OBJECTIVE: We evaluated somatosensory and motor interhemispheric integration in four patients who underwent transection of different portions of the anterior corpus callosum (CC) for removal of an intraventricular cyst. The study goal was to relate their performances to the topographical organization of the CC. METHODS: Experimental tasks included bimanual coordination, tactile cross-localization, and intermanual and interfield comparisons of somesthetic information. Response accuracy and response times were measured. In addition, interhemispheric transmission times were obtained in the somesthetic modality. RESULTS: Section of the middle portion of the genu caused a deficit in motor coordination, which was absent in patients with more posteriorly located lesions, whereas section of more rostral portions of the genu seemed to interfere with motor planning. The most posterior section in our sample, including the anterior portion of the body of the corpus, abolished interhemispheric transfer of simple somesthetic information (perception of touch) but not tactile discrimination (intermanual comparisons of shapes). We speculate that more complex somesthetic information is transferred through the caudal region of the body of the CC, which was spared in all patients. Thus, it seems that section of different portions of the anterior CC (genu and anterior body) produces specific deficits in interhemispheric integration in the motor and somesthetic modalities. These deficits are consistent with the anteroposterior topography of anterior callosal fibers. CONCLUSION: The specific disconnections deficits observed in this study may provide the surgeon with information regarding the consequences of anterior callosotomy and allow for remedial measures to be implemented if required.

Adult↗

PubMed2006

Visual and tactile learning of ground structures in desert ants.

Place defining landmarks that have been studied intensively in insect navigation are large, voluminous objects visible to the insect from quite some distance. Here, we show that in desert ants, Cataglyphis fortis, local variations in ground properties can also serve as landmarks. The ants were trained to forage within a linear channel, in which the floor adjacent to the nest entrance was altered in optical and tactile properties. When ants were later tested within a test channel that ran parallel to the training channel, they recognized this landmark and centred their search on the part of the ground structure during training that was closest to the nest entrance. Hence, physical properties of the ground can be learnt and used as cues defining, for example, the position of the nest. In a second series of experiments the ants were presented with ground structures that differed in their visual and tactile properties from the training structure. We show that the absence of either the correct tactile properties or the correct optical properties of the ground structure make the ants reject the previously accepted structure. Hence small ground structures are recognized by the ants as familiar landmarks only if both visual and tactile information coincides with what the ants have experienced during training.

Animals↗

PubMed2006

'Binaural echo disparity' as a potential indicator of object orientation and cue for object recognition in echolocating nectar-feeding bats.

Echolocating bats emit ultrasonic calls through their mouth or their nostrils and receive echoes from objects with both their ears. Information conveyed in the echoes is the basis for their three-dimensional acoustic perception of the surroundings. The direction of an object is encoded in binaural echo differences, i.e. on the one hand in the different arrival times of its echo at the two ears, and on the other hand in spectral differences through direction-dependent frequency filtering of head and pinnae. Insufficient attention has been paid, however, to the fact that three-dimensional objects produce structured spatial echo fields, and that the position of the ear in this field determines the echo it receives. We were interested to determine whether the two ears, in addition to direction-specific echo differences, receive object-specific echo disparities that might be useful for the bat. Our measurements with an artificial bat head, which consisted of two microphones and a small ultrasound loudspeaker arranged to resemble a bat's ears and mouth, revealed that echoes at the two ears differed largely depending on the shape and orientation of the echo-giving object. Binaural echo disparities of a bat-pollinated flower did indeed carry information about the orientation and, to a lesser extent, the shape of the flower. During flower approach such object-specific binaural echo disparities even exceed the binaural differences encoding direction of echo incidence, because the echo from the flower in front undergoes the same directional filtering by the two symmetrical ears. Nectar-feeding bats could use these object-specific binaural echo disparities not only to determine the object's orientation relative to the approaching bat, facilitating flight planning, but also to improve object recognition through spatial reconstruction of details of the object creating the echo. Our results suggest that the evaluation of binaural echo disparity has a greater importance for these tasks than has previously been assumed.

Animals↗

PubMed2006

Lack of generalization of object discrimination between spatial contexts by a bat.

Discrimination and generalization are important elements of cognition in the daily lives of animals. Nectar-feeding bats detect flowers by olfaction and probably vision, but also use echolocation and echo-perception of flowers in immediate target surroundings. The echo received from an interference-rich flower corolla is a function of a bat's own relative position in space. This raises the question how easily a free-flying bat will generalize an echo stimulus from a learning situation to a new spatial context where differences in relative flight approach trajectories may lead to an unfamiliar spectral composition of the self-generated echoes. We trained free-flying Glossophaga soricina in echoacoustic discrimination in a two-alternative forced-choice (2-AFC) paradigm at location A. We then tested at location B for spontaneous transfer of discrimination ability. Bats did not spontaneously transfer the discrimination ability acquired at A to location B. This lack of spontaneous generalization may have been caused by factors of the underlying learning mechanisms. 2-AFC tasks may not be representative of the natural foraging behaviour of flower-visiting bats. In contrast to insect-eating bats that constantly evaluate the environment to detect unpredictable prey, the spatial stability of flowers may allow flower visitors to rely on spatial memory to guide foraging. The 2-AFC task requires the disregard (learned irrelevance) of salient spatial location cues that are different at each new location. In Glossophaga, a conjunction between spatial context and 2-AFC discrimination learning may have inhibited the transfer of learned irrelevance of spatial location in the 2-AFC task to new spatial locations. Alternatively, the bats may have learnt the second discrimination task completely anew, and were faster only because of an acquired learning set. We suggest a dissociation between 2-AFC task acquisition and novel object discrimination learning to resolve the issue.

Animals↗

PubMed2005

Foveal contour interaction: detection and discrimination.

Contour interaction, the detrimental effect of flanking features on the discrimination of optotypes, has been studied mainly close to the visual acuity limit. We were interested to know how these results compare with those for the detection of targets. According to the simplest model of contour interaction, comparable detection effects would be expected. The case for low-level masking would be further strengthened if the form and nature of the dependence on flank separation and flank polarity followed that typically found in studies of lateral spatial masking [Vision Res. 33, 993 (1993)]. Landolt Cs subtending a visual angle of 0.25 degrees, 0.5 degrees, and 1.0 degrees were presented and contrast thresholds for detecting the presence of the Landolt C and discriminating its orientation were measured in five normal subjects as a function of flank separation and flank polarity. The results obtained for the relationship between detection and discrimination depend on the size of the target used. For small letters, discrimination but not detection was significantly affected by flanking bars. For large letters, detection and discrimination were affected to the same extent. However, in this case the effectiveness of opposite-polarity flanks and the finding that facilitation occurred at close, not far, flank separations suggests that the simplest explanation in terms of masking may not be applicable.

Differential Threshold↗

PubMed2006

Neuronal oscillations enhance stimulus discrimination by ensuring action potential precision.

Although oscillations in membrane potential are a prominent feature of sensory, motor, and cognitive function, their precise role in signal processing remains elusive. Here we show, using a combination of in vivo, in vitro, and theoretical approaches, that both synaptically and intrinsically generated membrane potential oscillations dramatically improve action potential (AP) precision by removing the membrane potential variance associated with jitter-accumulating trains of APs. This increased AP precision occurred irrespective of cell type and--at oscillation frequencies ranging from 3 to 65 Hz--permitted accurate discernment of up to 1,000 different stimuli. At low oscillation frequencies, stimulus discrimination showed a clear phase dependence whereby inputs arriving during the trough and the early rising phase of an oscillation cycle were most robustly discriminated. Thus, by ensuring AP precision, membrane potential oscillations dramatically enhance the discriminatory capabilities of individual neurons and networks of cells and provide one attractive explanation for their abundance in neurophysiological systems.

Action Potentials↗

PubMed2006

Robust filters for intensive care monitoring: beyond the running median.

Current alarm systems in intensive care units create a very high rate of false positive alarms because most of them simply compare physiological measurements to fixed thresholds. An improvement can be expected when the actual measurements are replaced by smoothed estimates of the underlying signal. However, classical filtering procedures are not appropriate for signal extraction, as standard assumptions, such as stationarity, do no hold here: the time series measured often show long periods without change, but also upward or downward trends, sudden shifts and numerous large measurement artefacts. Alternative approaches are needed to extract the relevant information from the data, i.e., the underlying signal of the monitored variables and the relevant patterns of change, such as abrupt shifts and trends. This article reviews recent research on filter-based online signal extraction methods designed for application in intensive care.

Algorithms↗

PubMed2006

Rapid brain discrimination of sounds of objects.

Electrical neuroimaging in humans identified the speed and spatiotemporal brain mechanism whereby sounds of living and man-made objects are discriminated. Subjects performed an "oddball" target detection task, selectively responding to sounds of either living or man-made objects on alternating blocks, which were controlled for in their spectrogram and harmonics-to-noise ratios between categories. Analyses were conducted on 64-channel auditory evoked potentials (AEPs) from nontarget trials. Comparing responses to sounds of living versus man-made objects, these analyses tested for modulations in local AEP waveforms, global response strength, and the topography of the electric field at the scalp. In addition, the local autoregressive average distributed linear inverse solution was applied to periods of observed modulations. Just 70 ms after stimulus onset, a common network of brain regions within the auditory "what" processing stream responded more strongly to sounds of man-made versus living objects, with differential activity within the right temporal and left inferior frontal cortices. Over the 155-257 ms period, the duration of activity of a brain network, including bilateral temporal and premotor cortices, differed between categories of sounds. Responses to sounds of living objects peaked approximately 12 ms later and the activity of the brain network active over this period was prolonged relative to that in response to sounds of man-made objects. The earliest task-related effects were observed at approximately 100 ms poststimulus onset, placing an upper limit on the speed of cortical auditory object discrimination. These results provide critical temporal constraints on human auditory object recognition and semantic discrimination processes.

Adult↗

PubMedDate not supplied

A comparison of word-recognition abilities assessed with digit pairs and digit triplets in multitalker babble.

This study compares, for listeners with normal hearing and listeners with hearing loss, the recognition performances obtained with digit-pair and digit-triplet stimulus sets presented in multitalker babble. Digits 1 through 10 (excluding 7) were mixed in approximately 1,000 ms segments of babble from 4 to -20 dB signal-to-babble (S/B) ratios, concatenated to form the pairs and triplets, and recorded on compact disc. Nine and eight digits were presented at each level for the digit-triplet and digit-pair paradigms, respectively. For the listeners with normal hearing and the listeners with hearing loss, the recognition performances were 3 dB and 1.2 dB better, respectively, on digit pairs than on digit triplets. For equal intelligibility, the listeners with hearing loss required an approximately 10 dB more favorable S/B than the listeners with normal hearing. The distributions of the 50% points for the two groups had no overlap.

Adult↗