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Test Stimuli (test + stimulus)
Selected AbstractsBehavioral relevance of gamma-band activity for short-term memory-based auditory decision-makingEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2008Jochen Kaiser Abstract Oscillatory activity in the gamma-band range has been established as a correlate of cognitive processes, including perception, attention and memory. Only a few studies, however, have provided evidence for an association between gamma-band activity (GBA) and measures of behavioral performance. Here we focused on the comparison between sample and test stimuli S1 and S2 during an auditory spatial short-term memory task. Applying statistical probability mapping to magnetoencephalographic recordings from 28 human subjects, we identified GBA components distinguishing nonidentical from identical S1,S2 pairs. This activity was found at frequencies between 65 and 90 Hz and was localized over posterior cortical regions contralateral to the hemifield in which the stimuli were presented. The 10 best task performers showed higher amplitudes of this GBA component than the 10 worst performers. This group difference was most pronounced between about 150 and 300 ms after stimulus onset. Apparently the decision about whether test stimuli matched the stored representation of previously presented sample sounds relied partly on the oscillatory activation of networks representing differences between both stimuli. This result could be replicated by reanalyzing the combined data from two previous studies assessing short-term memory for sound duration and sound lateralization, respectively. Similarly to our main study, GBA amplitudes to nonmatching vs. matching S1,S2 pairs were higher in good performers than poor performers. The present findings demonstrate the behavioral relevance of GBA. [source] Roles of the auditory cortex in discrimination learning by ratsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2006Kentaro Ono Abstract We investigated the roles of the auditory cortex in sound discrimination learning in Wistar rats. Absolute pitch or relative pitch can be used as discrimination cues in sound frequency discrimination. To clarify this, rats were trained to discriminate between rewarded (S+) and unrewarded (S,) test stimuli (S+ frequency > S, frequency). After learning was acquired by rats, performance was tested in a new test in which S+ frequency was constant but S+ frequency < S, frequency, or S+ frequency > S, frequency but both frequencies were increased. If the discrimination cue of the first test was preserved in the new test, performance following change of testing procedures was expected to remain high. The measured performance suggested that rats used relative pitch in half octave discrimination (difference between S+ and S, frequencies, 0.5 octave), and absolute pitch in octave discrimination (difference between S+ and S, frequencies, 1.0 octave). Bilateral lesions in the auditory cortex had almost no effect on performance before procedure change. Furthermore, performance following procedure change was not affected by lesions in the auditory cortex when the discrimination cue was preserved. However, performance was impaired by lesions in the auditory cortex when a new discrimination cue was used following procedure change. Lesions in the auditory cortex also impaired multimodal discrimination between sound and sound plus light. The present findings suggest that the auditory cortex plays a role as a sensory interface of the higher cortices required for flexible learning and multimodal discrimination. [source] An Insight into Forensic Document Examiner Expertise for Discriminating Between Forged and Disguised SignaturesJOURNAL OF FORENSIC SCIENCES, Issue 5 2008Adrian G. Dyer Ph.D. Abstract:, It has previously been shown that forensic document examiners (FDEs) have expertise in providing opinions about whether questioned signatures are genuine or simulated. This study extends the exploration of FDE expertise by evaluating the performance of eight FDEs and 12 control subjects at identifying signatures as either forgeries or the disguised writing of a specimen provider. Subject eye movements and response times were recorded with a Tobii 1750 eye tracker during the signature evaluations. Using a penalty scoring system, FDEs performed significantly better than control subjects (t = 2.465, p = 0.024), with one FDE able to correctly call 13 of the 16 test stimuli (and three inconclusive calls). An analysis of eye movement search patterns by the subjects indicated that a very similar search strategy was employed by both groups, suggesting that visual inspection of signatures is mediated by a bottom up search strategy. However, FDEs spent greater than 50% longer to make a decision than the control group. The findings are suggestive that for some stimuli FDEs can discriminate between forgeries and disguises, and that this ability is due to a careful inspection and consideration of multiple features within a signature. [source] Transient rise in intracellular calcium produces a long-lasting increase in plasma membrane calcium pump activity in rat sensory neuronsJOURNAL OF NEUROCHEMISTRY, Issue 4 2002William J. Pottorf II Abstract The plasma membrane Ca2+ ATPase (PMCA) plays a major role in clearing Ca2+ from the neuronal cytoplasm. Calmodulin stimulates PMCA activity and for some isoforms this activation persists following clearance of Ca2+ owing to the slow dissociation of calmodulin. We tested the hypothesis that PMCA-mediated Ca2+ efflux from rat dorsal root ganglion (DRG) neurons in culture would remain stimulated following increases in intracellular Ca2+ concentration ([Ca2+]i). PMCA-mediated Ca2+ extrusion was recorded following brief trains of action potentials using indo-1-based photometry in the presence of cyclopiazonic acid. A priming stimulus that increased [Ca2+]i to 506 ± 28 nm (>15 min) increased the rate constant for [Ca2+]i recovery by 47 ± 3%. Ca2+ clearance from subsequent test stimuli remained accelerated for up to an hour despite removal of the priming stimulus and a return to basal [Ca2+]i. The acceleration depended on the magnitude and duration of the priming [Ca2+]i increase, but was independent of the source of Ca2+. Increases in [Ca2+]i evoked by prolonged depolarization, sustained trains of action potentials or activation of vanilloid receptors all accelerated Ca2+ efflux. We conclude that PMCA-mediated Ca2+ efflux in DRG neurons is a dynamic process in which intense stimuli prime the pump for the next Ca2+ challenge. [source] Dentine hypersensitivity in subjects recruited for clinical trials: clinical evaluation, prevalence and intra-oral distributionJOURNAL OF ORAL REHABILITATION, Issue 3 2002D. G. Gillam Relatively few studies have reported on the frequency, distribution and severity of dentine hypersensitivity (DH) in subjects recruited for clinical trials of desensitizing agents. Potential subjects (n= 48 M, 81 F, mean age 35·1 years) for inclusion into such a study were screened to determine the extent of the problem. 117 subjects (41 M, 76 F) mean age 24·9 years were clinically examined. Evaluation by questionnaire indicated that the prevalence of DH was proportionately higher in the 20,29·9 years (34·9%), and 30,39·9 years groups (33·3%), respectively. Sensitivity to cold was the main presenting symptom. Tactile (probe) and cold air (dental air syringe) stimuli were used to clinically evaluate DH. Of the teeth eligible for evaluation 1561/3136 (49·8%) responded to either one or both of the test stimuli; 274/3136 (8·7%) responded to tactile only stimulation, 779/3136 (24·8%) to thermal only stimulation and 508/3136 (16·2%) to both tactile and thermal stimulation. Of those teeth responding to the stimuli, 477 (30·6%) were premolars, 437 (28%) incisors, 415 (26·8%) molars and 232 (14·9%) canines. The results agree with those of previously reported studies in that DH is most frequently observed on premolars and that proportionately more teeth are sensitive to evaporative than to tactile stimulation. Furthermore it would appear from the results of the study that tactile is less effective than thermal/evaporative stimulation in the evaluation of DH. [source] ASSESSMENT OF PREFERENCE WITH CONTROLS FOR RESPONSE BIAS OPERATING IN THE TEST SITUATION: A PRACTICAL EXAMPLE USING OMEGA-3 ENRICHED WHOLEGRAIN BREADS WITH ECUADORIAN CONSUMERSJOURNAL OF SENSORY STUDIES, Issue 5 2010YAMILLA ALVAREZ-COUREAUX ABSTRACT Ecuadorian consumers performed paired preference tests between sunflower rye bread and artisan wholegrain bread enriched with omega-3 fatty acids. Preferences for each were split fairly evenly. Further difference tests suggested that these preferences were elicited by visual rather than flavor/texture cues. The preference test included a "placebo" pair of "identical" stimuli to assess statistically whether the responses to the two test stimuli were merely because of response biases operating in the test situation and not differences in their sensory attributes. The concept of an "operational preference" was introduced to understand some of the ambiguities involved in the definition of preference. PRACTICAL APPLICATIONS The measurement of preference and acceptance of foods is important for product development and decisions regarding the launching of new products on to the market. The paired preference test has several problems associated with its design and analysis, and these are worthy of investigation. This article uses a practical example to illustrate some procedures developed as solutions to these challenges. Solutions to the problems involved in preference testing are essential so that the food industry can obtain trustworthy data. [source] A behavioural investigation of human visual short term memory for colourOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 5 2010V. A. Nemes Abstract We examined visual short term memory (VSTM) for colour using a delayed-match-to-sample paradigm. In these experiments we measured the effects of increasing inter-stimulus interval (ISI), varying between 0 and 10 s, on the ability of five colour normal human observers to make colour matches between a reference and subsequently presented test stimuli. The coloured stimuli used were defined by different chromatic axes on the isoluminant plane of DKL colour space. In preliminary experiments we used a hue scaling procedure to identify a total of 12 colour stimuli which served as reference hues in the colour memory experiments: four stimuli were exemplars of red, green, blue and yellow colour appearance categories, four were located between these categories and a further four were located on the cardinal axes that isolated the activity of the cone-opponent mechanisms. Our results demonstrate that there is a reduction in the ability of observers to make accurate colour matches with increasing ISIs and that this reduced performance was similar for all colour stimuli. However, the shifts in hue that were measured between the reference and matched test stimuli were significantly greater for the cardinal stimuli compared to those measured for the stimuli defined by the hue scaling procedure. This deterioration in the retention of hue in VSTM for stimuli that isolate cone-opponent mechanisms may be a reflection of the reorganisation of colour processing that occurs in the cortex where colour appearance mechanisms become more prominent. [source] Cortical processing of near-threshold tactile stimuli: An MEG studyPSYCHOPHYSIOLOGY, Issue 3 2010Anja Wühle Abstract In the present study we tested the applicability of a paired-stimulus paradigm for the investigation of near-threshold (NT) stimulus processing in the somatosensory system using magnetoencephalography. Cortical processing of the NT stimuli was studied indirectly by investigating the impact of NT stimuli on the source activity of succeeding suprathreshold test stimuli. We hypothesized that cortical responses evoked by test stimuli are reduced due to the preactivation of the same finger representation by the preceding NT stimulus. We observed attenuation of the magnetic responses in the secondary somatosensory (SII) cortex, with stronger decreases for perceived than for missed NT stimuli. Our data suggest that processing in the primary somatosensory cortex including recovery lasts for <200 ms. Conversely, the occupancy of SII lasts ,500 ms, which points to its role in temporal integration and conscious perception of sensory input. [source] The Effect of Prior Practice on Memory Reactivation and GeneralizationCHILD DEVELOPMENT, Issue 6 2003Harlene Hayne Three experiments examined the effect of practice on memory performance by 18-month-old infants. Infants were tested using an imitation paradigm; an adult demonstrated a series of actions with objects and infants were given the opportunity to reproduce those actions following a delay. Some infants practiced the target actions before the retention interval (practice) and some did not (no practice). In Experiment 1, a reminder treatment alleviated forgetting by infants who practiced but failed to alleviate forgetting by infants who did not practice. In Experiments 2A and 2B, infants who practiced generalized to novel test stimuli after a 24-hr delay, whereas infants without practice did not. Results suggest practice influences the accessibility and generality of infants' memories. [source] Somatosensory disinhibition in dystoniaMOVEMENT DISORDERS, Issue 4 2001Emma Frasson MD Abstract Despite the fact that somatosensory processing is inherently dependent on inhibitory functions, only excitatory aspects of the somatosensory feedback have so far been assessed in dystonic patients. We studied the recovery functions of spinal N13, brainstem P14, parietal N20, P27, and frontal N30 somatosensory evoked potentials (SEPs) after paired median nerve stimulation in 10 patients with dystonia and in 10 normal subjects. The recovery functions were assessed (conditioning stimulus: S1; test stimulus: S2) at interstimuls intervals (ISIs) of 5, 20, and 40 ms. SEPs evoked by S2 were calculated by subtracting the SEPs of the S1 only response from the SEPs of the response to the paired stimuli (S1 + S2), and their amplitudes were compared with those of the control response (S1) at each ISI considered. This ratio, (S2/S1)*100, investigates changes in the excitability of the somatosensory system. No significant difference was found in SEP amplitudes for single stimulus (S1) between dystonic patients and normal subjects. The (S2/S1)*100 ratio at the ISI of 5 ms did not significantly differ between dystonic patients and normal subjects, but at ISIs of 20 and 40 ms, this ratio was significantly higher in patients than in normals for spinal N13 and cortical N20, P27, N30 SEPs. These findings suggest that in dystonia there is an impaired inhibition at spinal and cortical levels of the somatosensory system which would lead to an abnormal sensory assistance to the ongoing motor programs, ultimately resulting in the motor abnormalities present in this disease. © 2001 Movement Disorder Society. [source] S-cone excitation ratios for reaction times to blue-yellow suprathreshold changes at isoluminanceOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 5 2010José M. Medina Abstract We examined different contrast metrics to scale visual latencies for suprathreshold stimuli modulated along tritan confusion lines. S-cone increments (,blue') and decrements (,yellow') were isolated along two different tritan confusion lines, each one having a different luminance value. Reaction times (RT) were evaluated as a function of the Weber contrast and the S-cone excitation ratio between the test stimulus and the background. RTs were described using a model that generalizes Piéron's law and incorporates the notion of threshold units and power law scaling. Our results show that RTs for S-cone increments and decrements equate better when using the S-cone excitation ratio. However, a single function did not describe all RT data. S-cone RTs are better described by separate functions. We conclude that S-cone increments and decrements do not scale in the same manner. Both Weber contrast and the S-cone excitation ratio are plausible metrics at isoluminance. The implications for the S-cone pathways are discussed. [source] Binocular interaction and performance of visual tasksOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 2 2004Maria S. Justo Abstract Binocular vision implies the fusion of the right and left retinal images to perceive a single image. For this, interocular interaction is required. We measured the reaction times to carry out a visual fixation task in order to determine whether binocular interaction influences performance. Several combinations of test and distraction stimuli were monocularly and binocularly presented to one monkey and three human subjects. The overall median reaction times were 340 ms for the animal and 308, 342 and 381 for human subjects 1, 2 and 3 respectively. Reaction time was shorter when the test stimulus was presented binocularly. Moreover, we observed that the presence of a distraction stimulus increased the reaction time and that a correlated distraction stimulus had a greater influence on this increase than an uncorrelated distraction stimulus. These findings indicate that with binocular vision a more rapid performance of a visual task occurs. [source] The response to paired motor cortical stimuli is abolished at a spinal level during human muscle fatigueTHE JOURNAL OF PHYSIOLOGY, Issue 23 2009Chris J. McNeil During maximal exercise, supraspinal fatigue contributes significantly to the decline in muscle performance but little is known about intracortical inhibition during such contractions. Long-interval inhibition is produced by a conditioning motor cortical stimulus delivered via transcranial magnetic stimulation (TMS) 50,200 ms prior to a second test stimulus. We aimed to delineate changes in this inhibition during a sustained maximal voluntary contraction (MVC). Eight subjects performed a 2 min MVC of elbow flexors. Single test and paired (conditioning,test interval of 100 ms) stimuli were delivered via TMS over the motor cortex every 7,8 s throughout the effort and during intermittent MVCs in the recovery period. To determine the role of spinal mechanisms, the protocol was repeated but the TMS test stimulus was replaced by cervicomedullary stimulation which activates the corticospinal tract. TMS motor evoked potentials (MEPs) and cervicomedullary motor evoked potentials (CMEPs) were recorded from biceps brachii. Unconditioned MEPs increased progressively with fatigue, whereas CMEPs increased initially but returned to the control value in the final 40 s of contraction. In contrast, both conditioned MEPs and CMEPs decreased rapidly with fatigue and were virtually abolished within 30 s. In recovery, unconditioned responses required <30 s but conditioned MEPs and CMEPs required ,90 s to return to control levels. Thus, long-interval inhibition increased markedly as fatigue progressed. Contrary to expectations, subcortically evoked CMEPs were inhibited as much as MEPs. This new phenomenon was also observed in the first dorsal interosseous muscle. Tested with a high intensity conditioning stimulus during a fatiguing maximal effort, long-interval inhibition of MEPs was increased primarily by spinal rather than motor cortical mechanisms. The spinal mechanisms exposed here may contribute to the development of central fatigue in human muscles. [source] Paired-pulse transcranial magnetic stimulation protocol applied to visual cortex of anaesthetized cat: effects on visually evoked single-unit activityTHE JOURNAL OF PHYSIOLOGY, Issue 3 2005Vera Moliadze In this study, we tested the paired-pulse transcranial magnetic stimulation (ppTMS) protocol , a conditioning stimulus (CS) given at variable intervals prior to a test stimulus (TS) , for visually evoked single-unit activity in cat primary visual cortex. We defined the TS as being supra-threshold when it caused a significant increase or decrease in the visually evoked activity. By systematically varying the interstimulus interval (ISI) between 2 and 30 ms and the strength of CS within the range 15,130% of TS, we found a clear dependence of the ppTMS effect on CS strength but little relation to ISI. The CS effect was strongest with an ISI of 3 ms and steadily declined for longer ISIs. A switch from enhancement of intracortical inhibition at short ISIs (2,5 ms, SICI) to intracortical facilitation (ICF) at longer ISIs (7,30 ms), as demonstrated for human motor cortex, was not evident. Whether the CS caused facilitation or suppression of the TS effect mainly depended on the strength of CS and the polarity of the TS effect: within a range of 60,130% a positive correlation between ppTMS and TS effect was evident, resulting in a stronger facilitation if the TS caused facilitation of visual activity, and more suppression if the TS was suppressive by itself. The correlation inverted when CS was reduced to 15,30%. The ppTMS effect was not simply the sum of the CS and TS effect, it was much smaller at weak CS strength (15,50%) but stronger than the sum of CS and TS effects at CS strength 60,100%. Differences in the physiological state between sensory and motor cortices and the interactions of paired synaptic inputs are discussed as possible reasons for the partly different effects of ppTMS in cat visual cortex and human motor cortex. [source] | |||||||||||||||||||