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PubMed1981

Visual signal detection and lambda responses.

On the basis of the result in earlier studies that the lambda response was associated with offset of the saccade, e.g., onset of the fixation pause, the relationship between the lambda response and the visual information processing load was examined. Eleven subjects were presented simultaneously random patterns including visual signals on Goldman perimeter and tone pips including auditory signals at random. In the visual task, the subject was instructed to search on the random pattern and detect the visual signals. In the auditory task, he was instructed to listen to tone pips without ceasing eye movements and detect the tone signals. EEGs from Oz and Cz, and the vertical and the horizontal EOGs were recorded. The vector EOG was calculated from both EOGs for detecting the absolute value of the saccade size. The occipital EEGs time-locked to offset of saccades were averaged 100 times to obtain lambda responses. The vertex EEGs time-locked to tone signals were averaged 100 times to obtain vertex potentials to auditory stimuli (AEP). Amplitudes of the lambda response (NOP100 and P100-N180) in the visual task were significantly higher than in the auditory task. Amplitudes of AEP (N1 and N1-P2) in the auditory task were enhanced significantly more than in the visual task. The results showed that the lambda response varied with information-processing load. The lambda response can be applicable as an index of visual information processing in eye movement situations.

Adult↗
PubMed1985

Signal detection in industrial noise: effects of noise exposure history, hearing loss, and the use of ear protection.

The detection of one-third octave signals superimposed on backgrounds of steady-state and intermittent industrial noise of 84 dBA was investigated for observers with normal hearing or moderate to severe noise-induced hearing loss (NIHL). Variables included age, noise exposure history, configuration of the audiogram and the wearing of insert hearing protectors. Detection thresholds were obtained binaurally over headphones using a two- interval forced-choice procedure. For unprotected listening all observers showed a masked threshold of about 80 dBA for a one-third octave band cented at 3.15 kHz. Neither variation in noise exposure history nor configuration of the audiogram were significant factors. Using insert protectors in noise, observers with normal hearing showed an advantage on average of 3 dB. Those with NIHL gave masked detection thresholds greater than 100 dBA. Detection of a one-third octave band centred at 1 kHz by hearing-impaired observers with mild to moderate loss at 1 kHz was similar to that for normal observers. A model of the detection process was developed and evaluated.

Adolescent↗
PubMed2003

Are VEP correlated fast optical signals detectable in the human adult by non-invasive nearinfrared spectroscopy (NIRS)?

The potential of near infrared spectroscopy (NIRS) to detect vascular changes in cerebral cortical tissue elicited by functional stimulation has been established (1). The vascular response is considered the result of neuronal activity in the investigated area and forms the basis of imaging techniques such as BOLD-contrast fMRI and PET. In the animal optical methods have been shown to detect optical changes in the illuminated tissue which exactly follow the time course of electrical potential changes, thus optical techniques can potentially assess both the 'fast' neuronal and the 'slow' vascular response. Lately a group of investigators has reported data showing that the 'fast optical signal' is detectable in the adult human in response to a visual stimulus ("optical VEP" termed EROS, i.e. event related optical signal). We failed to reproduce these results, with an almost identical instrumentation and experimental protocol. The negative result is reported in this paper. To check the expected magnitude of such changes we performed a simulation based on data reported in the animal and a human head model of optical properties. The result indicates that changes in optical properties to be expected in a non-invasive approach in the human adult are about three orders of magnitude smaller than those reported previously by the group of Gratton and co-workers (2). Also they are so small that they are below the noise level of the presently available NIRS monitors.

Adult↗
PubMed1990

Efficient across-frequency integration in short-signal detection.

A series of experiments was performed on the influence of bandwidth on the masked threshold of brief deterministic signals in continuous broadband noise. The signal bandwidth is quantified by the number (n) of constituent 1/3-oct bands. For n increasing from 1 to typically 9, the masked-threshold level in the constituent 1/3-oct bands is found to decrease by 8 log(n). This integration rule is obtained when each of the 1/3-oct bands covered by the signal equally contributes to detection, i.e., that, for each of these 1/3-oct bands, the difference between signal level and the individual masked-threshold level is the same. It was found that this integration rule also applies to noncontiguous signal spectra and that it remains intact over a broad range of masker levels. Commonly, the masked threshold of compound signals (for instance, n frequency components with a spacing of typically 1/3 oct), relative to the masked threshold of single-component signals, has been described by a 5 log(n) integration rule. However, this rule was obtained for signal durations of typically 100 ms or more. For the present brief signals (typically 10 ms or less), the across-frequency integration is found to be more effective.

Acoustic Stimulation↗
PubMed2005

Dual antiplatelet therapy with clopidogrel and aspirin in symptomatic carotid stenosis evaluated using doppler embolic signal detection: the Clopidogrel and Aspirin for Reduction of Emboli in Symptomatic Carotid Stenosis (CARESS) trial.

BACKGROUND: Evidence for efficacy of dual antiplatelet therapy in stroke is limited. Symptomatic carotid stenosis patients are at high risk of early recurrent stroke. In this group, asymptomatic microembolic signals (MES), detected by transcranial Doppler ultrasound (TCD), are markers of future stroke and transient ischemic attack (TIA) risk. They offer a surrogate marker to evaluate antiplatelet therapy, but no multicenter study has evaluated the feasibility of this approach. METHODS AND RESULTS: Clopidogrel and Aspirin for Reduction of Emboli in Symptomatic Carotid Stenosis (CARESS) is a randomized, double-blind study in subjects with recently symptomatic > or =50% carotid stenosis. Patients were screened with TCD, and if MES were detected, they were randomized to clopidogrel and aspirin or aspirin monotherapy. Repeated TCD recordings were made on days 2 and 7. MES were detected in 110 of 230 patients by online analysis at baseline, of whom 107 were randomized. Intention-to-treat analysis revealed a significant reduction in the primary end point: 43.8% of dual-therapy patients were MES positive on day 7, as compared with 72.7% of monotherapy patients (relative risk reduction 39.8%; 95% CI, 13.8 to 58.0; P=0.0046). The secondary end point of MES frequency per hour was reduced (compared with baseline) by 61.4% (95% CI, 31.6 to 78.2; P=0.0013) in the dual-therapy group at day 7 and by 61.6% (95% CI, 34.9 to 77.4; P=0.0005) on day 2. There were 4 recurrent strokes and 7 TIAs in the monotherapy group versus no stroke and 4 TIAs in the dual-therapy group that were treatment emergent and ipsilateral to the qualifying carotid stenosis; 2 additional ipsilateral TIAs occurred before treatment started. MES frequency was greater in the 17 patients with recurrent ipsilateral events compared with the 90 without (mean+/-SD: 24.4+/-27.7 versus 8.9+/-11.5 per hour; P=0.0003). CONCLUSIONS: In patients with recently symptomatic carotid stenosis, combination therapy with clopidogrel and aspirin is more effective than aspirin alone in reducing asymptomatic embolization. Doppler MES detection is a feasible method to evaluate the efficacy of antiplatelet therapy in multicenter studies.

Aged↗
PubMed1975

Auditory signal detectability and facilitation of simple reaction time in psychiatric patients and non-patients.

Patients diagnosed on the basis of structured interviews as having affective psychoses were less sensitive in detecting the presence of a transient auditory signal than were schizophrenic patients or non-patients. Patients with affective psychoses also benefited more (their reaction time was more reduced) than the other two groups from the presence of a second auditory transient.

Acoustic Stimulation↗
PubMed1989

A comparison of signal detection between an echolocating dolphin and an optimal receiver.

An electronic simulated target apparatus was used in a two-experiment study to compare the target detection performance of an echolocating bottlenose dolphin with an optimal receiver. Random Gaussian noise with a relatively flat spectrum from 20 to 160 kHz was used as a masking source. Experiment I was conducted to establish a technique for estimating the echo energy-to-noise ratio, Ee/N, at the dolphin's threshold of detection. Dolphins typically vary the amplitude of their emitted signal over a large range making it difficult to estimate Ee/N. In the first part of experiment I, the simulated echo was a double click, the pulses separated by 200 microseconds, with each pulse being a replica of the dolphin's transmitted signal. A staircase psychophysical procedure was used to obtain the detection threshold, and the echo energy-to-noise ratio based on the highest amplitude click emitted per trial, (Ee/N)max, was determined at each reversal point. The second echo type consisted of one of the animal's echolocation clicks, previously measured, digitized and stored in an erasable programmable read-only memory (EPROM). The electronic target simulator was modified so that every time the dolphin emitted an echolocation signal, the EPROM was triggered to produce two pulses separated by 200 microseconds. On any trial, the EPROM signal was played back at a fixed amplitude, regardless of the amplitude of the dolphin's emitted signal. The Ee/N obtained with the EPROM signal at threshold was found to be 2.9 dB lower than (Ee/N)max obtained with the normal phantom target. Therefore an estimate of Ee/N can be obtained by subtracting 2.9 dB from (Ee/N)max.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Local subplasma membrane Ca2+ signals detected by a tethered Ca2+ sensor.

Accumulating evidence indicates that plasma membrane (PM) microdomains and the subjacent "junctional" sarcoplasmic/endoplasmic reticulum (jS/ER) constitute specialized Ca(2+) signaling complexes in many cell types. We examined the possibility that some Ca(2+) signals arising in the junctional space between the PM and jS/ER may represent cross-talk between the PM and jS/ER. The Ca(2+) sensor protein, GCaMP2, was targeted to different PM domains by constructing genes for fusion proteins with either the alpha1 or alpha2 isoform of the Na(+) pump catalytic (alpha) subunit. These fusion proteins were expressed in primary cultured mouse brain astrocytes and arterial smooth muscle cells. Immunocytochemistry demonstrated that alpha2(f)GCaMP2, like native Na(+) pumps with alpha2-subunits, sorted to PM domains that colocalized with subjacent S/ER; alpha1(f)GCaMP2, like Na(+) pumps with alpha1-subunits, was more uniformly distributed. The GCaMP2 moieties in both constructs were tethered just beneath the PM. Both constructs detected global Ca(2+) signals evoked by serotonin (in arterial smooth muscle cells) and ATP, and by store-operated Ca(2+) channel-mediated Ca(2+) entry after S/ER unloading with cyclopiazonic acid (in Ca(2+)-free medium). When cytosolic Ca(2+) diffusion was markedly restricted with EGTA, however, only alpha2(f)GCaMP2 detected the local, store-operated Ca(2+) channel-mediated Ca(2+) entry signal. Thus, alpha1 Na(+) pumps are apparently excluded from the PM microdomains occupied by alpha2 Na(2+) pumps. The jS/ER and adjacent PM may communicate by Ca(2+) signals that are confined to the tiny junctional space between the two membranes. Similar methods may be useful for studying localized Ca(2+) signals in other subPM microdomains and signals associated with other organelles.

Adenosine Triphosphate↗
PubMed2000

Visual signal detection in structured backgrounds. III. Calculation of figures of merit for model observers in statistically nonstationary backgrounds.

Models of human visual detection have been successfully used in computer-generated noise. For these backgrounds, which are generally statistically stationary, model performance can be readily calculated by computing the index of detectability d' from the noise power spectrum, the signal profile, and the model template. However, model observers are ultimately needed in more real backgrounds, which may be statistically non-stationary. We investigated different methods to calculate figures of merit for model observers in real backgrounds based on different assumptions about image stationarity. We computed performance of the nonpre-whitening matched-filter observer with an eye filter on mammography and coronary angiography for an additive or a multiplicative signal. Performance was measured either by applying the model template to the images or by computing closed-form expressions with various assumptions about image stationarity. Results show first that the structured backgrounds investigated cannot be considered stationary. Second, traditional closed-form expressions of detectability calculated from the noise power spectra with the assumption of background stationarity lead to erroneous estimates of model performance. Third, the most accurate way of measuring model performances is by directly applying the model template on the images or by computing a closed-form expression that does not assume image stationarity.

Choice Behavior↗
PubMed2004

Sum-difference theory of remembering and knowing: a two-dimensional signal-detection model.

In the remember-know paradigm for studying recognition memory, participants distinguish items whose presentations are episodically remembered from those that are merely familiar. A one-dimensional model postulates that remember responses are just high-confidence old judgments, but a meta-analysis of 373 experiments shows that the receiver operating characteristic (ROC) curves predicted by this model have the wrong slope. According to the new sum-difference Theory of remembering and knowing (STREAK), old items differ from new ones in both global and specific memory strength: The old-new judgment is based on a weighted sum of these dimensions, and the remember- know judgment is based on a weighted difference. STREAK accounts for the form of several novel kinds of ROC curves and for existing remember-know and item-recognition data.

Humans↗
PubMed2002

Two bs or not two Bs? A signal detection theory analysis of repetition blindness in a counting task.

Stimulus repetition usually benefits performance. A notable exception is repetition blindness (RB), in which subjects fail to report a repeated stimulus in a rapid serial visual presentation. Theories differ in attributing RB to either perceptual encoding or memory retrieval and to impaired discrimination versus response bias. In the present study, subjects judged whether one or two letters were imbedded in sequences of digits. Unlike previous studies, false guesses of two unrepeated letters were distinguished from false guesses of two repeated letters. When repeated- and unrepeated-letter trials were randomly intermixed (Experiment 1), RB was entirely attributable to response bias. However, when they were separately blocked (Experiments 2 and 3), RB was manifested in discriminability (d'). The results support perceptual-encoding accounts of RB but indicate that effects on discriminability depend on subjects' processing strategies.

Cognition↗
PubMed2006

Phantom ROC: Recollection rejection in a hybrid conjoint recognition signal detection model.

The present experiments test predictions of dual process models with regards to recollection rejection using a model called phantom ROC. Participants studied pictures and then took a recognition test in which they were presented with targets (i.e., the exact picture presented), related lures (i.e., the same object but from a different angle), and unrelated lures (i.e., objects that had not been shown). For each item, participants answered both standard recognition and meaning recognition questions. In Experiment 1 participants studied pictures under either full attention or divided attention. In Experiment 2 some participants were told that no object was shown twice (i.e., mutual exclusivity instructions), while others were told that both camera angles might have been shown for some objects (no mutual exclusivity instructions). The present experiments provide three converging measures, all of which are consistent with dual process models that propose a recollection rejection mechanism.

Attention↗