Biomedical subjects

W Ritter

Publications and source records attributed to W Ritter.

At least 37 records · Page 2Linked to original sources

PubMed1999

Changes in sensitivity to stimulus deviance in Alzheimer's disease: an ERP perspective.

The mismatch negativity (MMN) of the event-related brain potential (ERP) reflects the storage of information in sensory memory. MMNs were recorded from eight patients with Alzheimer's disease (AD) and eight controls to small (delta50 Hz), large (delta300 Hz), and a variety of highly deviant, environmental sounds. Both old controls and patients showed robust MMNs to all three classes of deviant events, and robust P3 compounds (indicative of active attention) to the environmental sounds. The data suggest that patients with mild AD have an intact sensory memory mechanism that responds similarly to that of controls to systematic increases in deviance. However, for both older controls and patients, only highly deviant acoustic events are likely to involuntary capture attention.

Acoustic Stimulation↗

PubMed1999

The lifetime of automatic semantic priming effects may exceed two seconds.

The N400 component of event-related potentials (ERPs) was obtained in a modified version of the Neely [J.H. Neely, Semantic priming and retrieval from lexical memory: Roles of inhibitionless spreading activation and limited-capacity attention, Journal of Experimental Psychology: General, Vol. 106 (1977), pp. 226-254.] paradigm which permits unconfounding of semantic priming effects due to automatic and attentional processes. It was found that a short stimulus onset asynchrony (SOA) of 250 ms between the prime and the target was associated with automatic but not expectancy effects on the amplitude of N400. At a long SOA of 2000 ms between prime and target, semantic priming effects on N400 were obtained associated with both automatic and expectancy processes. Moreover, there was no significance difference in the magnitude of the automatic effects at the two SOAs, suggesting that automatic processing had not decayed within the 2000 ms interval between the prime and target. The results support the two-processing interpretation of semantic priming advanced by Posner and Synder [M.I. Posner, C.R.R. Snyder, Attention and cognitive control, in: R.L. Solso (Ed.), Information Processing and Cognition: The Loyola Symposium, Erlbaum, Hillsdale, NJ (1975).] and concur with the results of Neely [J.H. Neely, Semantic priming and retrieval from lexical memory: Roles of inhibitionless spreading activation and limited-capacity attention, Journal of Experimental Psychology: General, Vol. 106 (1977), pp. 226-254], with the exception of indicating a longer persistence of automatic processes.

Adult↗

PubMed1999

An investigation of the auditory streaming effect using event-related brain potentials.

There is uncertainty concerning the extent to which the auditory streaming effect is a function of attentive or preattentive mechanisms. The mismatch negativity (MMN), which indexes preattentive acoustic processing, was used to probe whether the segregation associated with the streaming effect occurs preattentively. In Experiment 1, alternating high and low those were presented at fast and slow paces while subjects ignored the stimuli. At the slow pace, tones were heard as alternating high and low pitches, and no MMN was elicited. At the fast pace a streaming effect was induced and an MMN was observed for the low stream, indicating a preattentive locus for the streaming effect. The high deviant did not elicit an MMN. MMNs were obtained to both the high and low deviants when the interval between the across-stream deviance was lengthened to more than 250 ms in Experiment 2, indicating that the MMN system is susceptible to processing constraints.

Acoustic Stimulation↗

PubMed1999

Electrophysiological evidence of developmental changes in the duration of auditory sensory memory.

In behavioral studies, children's memory for tonal frequency has been found to persist for less time than adults' (T. A. Keller & N. Cowan, 1994). The present study was done to evaluate the argument that this effect is due to changes in auditory sensory memory and not to attentional mechanisms. This question was investigated using mismatch negativity (MMN), an auditory event-related potential considered to be insensitive to attention. Participants were 6-7-, 8-10-, and 11-12-year-old children and adults. They were presented with trains of stimuli, beginning with either a standard (1000 Hz) or a deviant (1200 Hz) tone with trains separated by either 1 s or 8 s. All 4 groups exhibited MMNs after delays of 1 s, but only the adults and oldest children exhibited MMNs after 8 s, indicating that there are maturational changes in the duration of auditory sensory memory.

Acoustic Stimulation↗

PubMed1999

Normal time course of auditory recognition in schizophrenia, despite impaired precision of the auditory sensory ("echoic") memory code.

Prior studies have demonstrated impaired precision of processing within the auditory sensory memory (ASM) system in schizophrenia. This study used auditory backward masking to evaluate the degree to which such deficits resulted from impaired overall precision versus premature decay of information within the short-term auditory store. ASM performance was evaluated in 14 schizophrenic participants and 16 controls. Schizophrenic participants were severely impaired in their ability to match tones following delay. However, when no-mask performance was equated across participants, schizophrenic participants were no more susceptible to the effects of backward maskers than were controls. Thus, despite impaired precision of ASM performance, schizophrenic participants showed no deficits in the time course over which short-term representations could be used within the ASM system.

Acoustic Stimulation↗

PubMed1999

Episodic priming and memory for temporal source: event-related potentials reveal age-related differences in prefrontal functioning.

Event-related potentials (ERPs) were recorded from young (M = 25) and older (M = 71) adults during a recognition memory paradigm that assessed episodic priming. Participants studied two temporally distinct lists of sentences (each with two unassociated nouns). At test, in response to the nouns, participants made old-new, followed by remember (context)-know (familiarity) and source (i.e., list) judgments. Both young and older adults showed equivalent episodic priming effects. However, compared to the young adults, the older adults showed a greater source performance decrement than item memory performance decrement. Both age groups showed equivalent posterior-maximal old-new ERP effects. However, only the young produced a frontal-maximal, late onset old-new effect that differed as a function of subsequent list attribution. Because source memory is thought to be mediated by prefrontal cortex, we conclude that age-related memory differences may be due to a deficit in a prefrontal cortical system that underlies source memory and are not likely to be due to an age-related decline in episodic priming.

Adult↗

PubMed1999

Triple images on panoramic radiographs.

OBJECTIVE: To explain the formation of triple images on panoramic radiographs. METHODS: A metal test object was placed in defined positions in relation to movement path of a panoramic X-ray beam. RESULTS: The test object was portrayed once, twice or three times with varying degrees of distortion depending on its location. Triple images were formed when the test object was located in a specific diamond-shaped area distal to the path of the rotation centre of the X-ray beam. CONCLUSIONS: The formation of triple images on panoramic radiographs can be explained on the basis of known projection geometry.

Artifacts↗

PubMed1999

Two cognitive systems simultaneously prepared for opposite events.

Event-related potentials (ERPs) were recorded during a go/no-go reaction time (RT) task in which subjects responded to rare target tones and withheld response to frequent tones. In a predictable condition, a rare visual stimulus signalled the impending occurrence of a rare tone, whereas a frequent visual stimulus signalled that a frequent tone would be presented. The rare visual stimuli elicited P3, associated with violations of expectations, whereas the rare tones, being predictable, did not. The rare tones elicited the mismatch negativity (MMN), a component associated with preattentive deviance detection, despite the fact that they were expected. RT was faster in the predictable condition than in another condition in which the tones were not predictable. The P3 and RT data indicate, respectively, that subjects anticipated and were ready to respond to the target tones. The MMN result indicates that immediately before target tones, the preattentive system underlying the MMN was set for frequent tones, being unaffected by the information available to the higher order system. Thus, the higher order cognitive system associated with P3 and the lower order cognitive system associated with the MMN were prepared simultaneously for opposite events.

Acoustic Stimulation↗

PubMed1998

Predictability of stimulus deviance and the mismatch negativity.

The purpose of this study was to test the previous report that generation of the mismatch negativity (MMN) component of event-related brain potentials (ERPs) is indifferent to the predictable occurrence of stimulus deviance. A pattern of standards (S) and deviants (D) were delivered in a predictable fashion (SSSSD) at two different speeds (1.3 s and 100 ms). An MMN was obtained to the D position tone at the slow but not the fast pace. These results demonstrate that, unlike the P3 component, the MMN is sensitive to the predictable occurrence of stimulus deviance when the predictability can be detected by the brain within the estimated limits of sensory memory.

Acoustic Stimulation↗

PubMed1998

Feature conjunctions and auditory sensory memory.

This study sought to obtain additional evidence that transient auditory memory stores information about conjunctions of features on an automatic basis. The mismatch negativity of event-related potentials was employed because its operations are based on information that is stored in transient auditory memory. The mismatch negativity was found to be elicited by a tone that differed from standard tones in a combination of its perceived location and frequency. The result lends further support to the hypothesis that the system upon which the mismatch negativity relies processes stimuli in an holistic manner.

Acoustic Stimulation↗

PubMed1998

Attention affects the organization of auditory input associated with the mismatch negativity system.

The mismatch negativity (MMN), a component of event-related potentials (ERP), was used to investigate the effect of attention on auditory stream segregation. Subjects were presented with sequences of alternating high and low tones that occurred at a constant rate, which they ignored. When subjects ignored the stimuli, the three-tone standard and deviant sequences contained within the high- and low-pitched tones did not emerge and no MMNs were obtained. Subjects were then instructed to attend to the high-pitched tones of the stimulus sequences and detect the within-stream deviants. When subjects selectively attended the high-pitched tones, MMNs were obtained to the deviants within both the attended and unattended streams. These results indicate that attention can produce segregation such that the sequences of low- and high-pitched tones are available to the automatic deviance detection system that underlies the generation of the MMN. Selective attention can alter the organization of sensory input in the early stages of acoustic processing.

Acoustic Stimulation↗

PubMed1998

Impaired mismatch negativity (MMN) generation in schizophrenia as a function of stimulus deviance, probability, and interstimulus/interdeviant interval.

Schizophrenia is a severe mental disorder associated with disturbances in perception and cognition. Event-related potentials (ERP) provide a mechanism for evaluating potential mechanisms underlying neurophysiological dysfunction in schizophrenia. Mismatch negativity (MMN) is a short-duration auditory cognitive ERP component that indexes operation of the auditory sensory ('echoic') memory system. Prior studies have demonstrated impaired MMN generation in schizophrenia along with deficits in auditory sensory memory performance. MMN is elicited in an auditory oddball paradigm in which a sequence of repetitive standard tones is interrupted infrequently by a physically deviant ('oddball') stimulus. The present study evaluates MMN generation as a function of deviant stimulus probability, interstimulus interval, interdeviant interval and the degree of pitch separation between the standard and deviant stimuli. The major findings of the present study are first, that MMN amplitude is decreased in schizophrenia across a broad range of stimulus conditions, and second, that the degree of deficit in schizophrenia is largest under conditions when MMN is normally largest. The pattern of deficit observed in schizophrenia differs from the pattern observed in other conditions associated with MMN dysfunction, including Alzheimer's disease, stroke, and alcohol intoxication.

Acoustic Stimulation↗

PubMed1998

[Imaging of aortic endoprostheses and their complications].

PURPOSE: To determine the optimal postoperative imaging modality for the follow-up of patients with endoluminal aortic stent grafts. MATERIAL AND METHODS: From August 1994 to November 1997, 214 patients (194 male and 20 female) with abdominal and thoracic aortic aneurysms were treated with endovascular stent grafts. 137 patients (129 male, 8 female) with 89 tube grafts and 48 bifurcated grafts (45 EVT, 88 Stentor/Vanguard, 3 Chuter, 1 Talent) were evaluated with contrast-enhanced spiral-CT, duplex ultrasound, and DSA at a mean follow-up of 11.1 months. RESULTS: We found 12 persistent primary endoleaks (8.8%), 17 secondary endoleaks (12.4%), 8 limb occlusions (5.8%), 28 endoluminal thrombi lining the stent graft (20.4%), and 26 suture breakages of the stent frame (19%). In 9 patients (6.6%) the proximal end of the stent partially covered the renal arteries. In 3 patients (2.2%) a partial renal infarction was seen. Spiral-CT was able to demonstrate all the above changes except for 3 sidebranch endoleaks that were documented by duplex ultrasound only and 8 suture breaks seen on abdominal plain films only. The median aneurysm diameter decreased from 48 mm pre-operatively to 46 mm at 24 months post-operatively in patients with endoleaks and from 44 mm to 36 mm in patients without endoleak. For several patients the decreasing aneurysm diameter did not reliably correlate with complete exclusion of the aneurysm. CONCLUSION: For follow-up of endoluminal aortic stent grafts contrast-enhanced spiral-CT is superior to duplex ultrasound. DSA is necessary only for patients with complications requiring a secondary intervention.

Adult↗

PubMed1998

Reactivation of a dormant representation of an auditory stimulus feature.

Research with the mismatch negativity component of event-related potentials has uncovered a system that detects change in the acoustic environment on an automatic basis. The system is considered to compare incoming stimuli to representations of the past and to emit an MMN if change is detected. Previous investigations have shown that the relevant memory of the past can become dormant and then be reactivated by a reminder stimulus. It is unclear, however, whether what is reactivated is an holistic representation of stimuli or separate representations of features of stimuli. The present study provides data that supports the latter possibility but leaves open the former one.

Acoustic Stimulation↗

PubMed1998

Automatic change detection: does the auditory system use representations of individual stimulus features or gestalts?

The effects of global and feature-specific probabilities of auditory stimuli were manipulated to determine their effects on the mismatch negativity (MMN) of the human event-related potential. The question of interest was whether the automatic comparison of stimuli indexed by the MMN was performed on representations of individual stimulus features or on gestalt representations of their combined attributes. The design of the study was such that both feature and gestalt representations could have been available to the comparator mechanism generating the MMN. The data were consistent with the interpretation that the MMN was generated following an analysis of stimulus features.

Adult↗

PubMed1997

Item and source memory: differential age effects revealed by event-related potentials.

The neural substrates of age-related memory differences were evaluated by recording event-related potentials (ERPs) from young and older adults during a recognition memory paradigm. Subjects studied two temporally distinct lists of sentences (each with two nouns) and were tested for their memory of the nouns and of the list (i.e. temporal source) in which they had occurred. Compared with the young, the old showed a greater source than item memory performance decrement. Both age groups showed equivalent posterior-maximal old/new ERP effects. However, only the young produced a frontal-maximal, late onset old/new effect that differed as a function of subsequent source attribution. Age-related explicit memory differences may be due to a deficit in a prefrontal cortical system that underlies source memory.

Adult↗

PubMed1997

Mismatch negativity during attend and ignore conditions in Alzheimer's disease.

Mismatch negativities (MMNs) of the event-related potential to deviant tones and environmental sounds were recorded during active and ignore oddball sequences in young and elderly controls and patients with probable Alzheimer's disease (PAD). MMNs were smaller in the PAD waveforms compared to those of the controls, suggesting a degraded sensory memory trace in these subjects; however, under ignore conditions, environmental sounds elicited robust MMNs in the PAD group along with N2b and novelty P3 components in similar fashion to controls. As N2b and P3 are usually elicited by attended stimuli, these data suggest that in the PAD subjects, the highly deviant events involuntarily captured attention, perhaps reflecting the activation of an attentional switching mechanism. Because this passive switching is thought to reflect activation of a mechanism located in the frontal lobes, the data suggest that this putative frontal lobe mechanism is relatively intact in the early stages of the disease.

Acoustic Stimulation↗

PubMed1997

Multiple visuospatial working memory buffers: evidence from spatiotemporal patterns of brain activity.

Numerous studies have shown that the visual system involves different cortical pathways in the perception of object (ventral visual pathway) and spatial (dorsal visual pathway) information. The present study was concerned with whether human visuospatial working memory divides along similar lines. We used event-related brain potentials (ERPs) recorded from scalp of normal humans to show the existence of different buffering systems for the retention of object and spatial visual information. Subjects were presented with object or spatial stimuli to be retained for a 3.6-sec interval. The ERPs isolated brain activity associated with retention from earlier storage and later retrieval processes. The ERP scalp topographies indicated that the underlying patterns of brain activation were different during retention of object and spatial information.

Adult↗