Interstimulus Interval Conditions Research Articles

The effects of aging on lifetime of auditory sensory memory in humans

The amplitude change of cortical responses to repeated stimulation with respect to different interstimulus intervals (ISIs) is considered as an index of sensory memory. To determine the effect of aging on lifetime of auditory sensory memory, N100m responses were recorded in young, middle-aged, and elderly healthy volunteers (n=15 for each group). Trains of 5 successive tones were presented with an inter-train interval of 10s. In separate sessions, the within-train ISIs were 0.5, 1, 2, 4, and 8s. The amplitude ratio between N100m responses to the first and fifth stimuli (S5/S1 N100m ratio) within each ISI condition was obtained to reflect the recovery cycle profile. The recovery function time constant (τ) was smaller in the elderly (1.06±0.26s, p<0.001) and middle-aged (1.70±0.25s, p=0.009) groups compared with the young group (2.77±0.25s). In conclusion, the present study suggests an aging-related decrease in lifetime of auditory sensory memory.

Change‐related responses in the human auditory cortex: An MEG study

We recorded cortical activity in response to the onset, offset, and frequency change of a pure tone using magnetencephalograms (MEGs) to clarify the physiological significance of N1m relating to the detection of changes. Four interstimulus intervals (ISIs) (0.5, 1.5, 3, and 6 s) were used for each of the three auditory events. Results showed that (i) all three auditory events elicited N1m with a similar topography and similar temporal profile, (ii) the source of N1m was located in the superior temporal gyrus (STG) for all events under all ISI conditions, (iii) the amplitude of the STG activity as a function of the duration of the steady state preceding the change was similar among the three events, and (iv) there was a significant positive correlation in amplitude between on-N1m and off-N1m and between on-N1m and change-N1m. These results suggested that N1m for the three events has a similar physiological significance relating to the detection of changes.

Hemispheric asymmetries in processing L1 and L2 idioms: Effects of salience and context

This study investigates the contribution of the left and right hemispheres to the comprehension of bilingual figurative language and the joint effects of salience and context on the differential cerebral involvement in idiom processing. The divided visual field and the lexical decision priming paradigms were employed to examine the activation of salient and nonsalient ambiguous idiom interpretations (i.e., literal vs. non-literal) in the two hemispheres. Literally plausible ambiguous idioms, L1 (Polish) and L2 (English), were embedded in unconstraining ambiguous (e.g., I knew he kept an ace up his sleeve) or constraining unambiguous context clearly favoring their conventional idiomatic interpretation (e.g., The debating president kept an ace up his sleeve). Idioms were presented centrally, followed by laterally presented targets related to the figurative (e.g., GAIN) or literal (e.g., SHIRT) meaning of the idiom and displayed at Interstimulus Intervals (ISIs) of 0 ms (Experiment 1), 300 ms (Experiment 2), and 800 ms (Experiment 3). Results indicate that context and salience effects are significantly modulated by the language (native vs. nonnative) of the stimulus materials being presented to each hemisphere. Literal facilitation was found for L2 idioms in all three ISI conditions, which supports the notion of the special status that literal meanings of L2 idioms enjoy in the course of their processing by nonnative language users. No significant differences were found between the right and left hemispheres in regards to their sensitivity to contextual constraints. Results are discussed in terms of the Graded Salience Hypothesis and the Fine/Coarse Coding Theory.

Retention Interval Affects Visual Short-Term Memory Encoding

Humans can efficiently store fine-detailed facial emotional information in visual short-term memory for several seconds. However, an unresolved question is whether the same neural mechanisms underlie high-fidelity short-term memory for emotional expressions at different retention intervals. Here we show that retention interval affects the neural processes of short-term memory encoding using a delayed facial emotion discrimination task. The early sensory P100 component of the event-related potentials (ERP) was larger in the 1-s interstimulus interval (ISI) condition than in the 6-s ISI condition, whereas the face-specific N170 component was larger in the longer ISI condition. Furthermore, the memory-related late P3b component of the ERP responses was also modulated by retention interval: it was reduced in the 1-s ISI as compared with the 6-s condition. The present findings cannot be explained based on differences in sensory processing demands or overall task difficulty because there was no difference in the stimulus information and subjects' performance between the two different ISI conditions. These results reveal that encoding processes underlying high-precision short-term memory for facial emotional expressions are modulated depending on whether information has to be stored for one or for several seconds.

Timing of conditioned eyeblink responses is impaired in children with attention-deficit/hyperactivity disorder

Structural changes of the cerebellum have been reported in several psychiatric diseases like schizophrenia, autism and attention-deficit/hyperactivity disorder (ADHD). Beside behavioral deficits children with ADHD often show slight motor abnormalities. Cerebellar malfunction may contribute. The cerebellum is a structure essential for motor coordination, various forms of motor learning and timing of motor responses. In the present study, eyeblink conditioning was applied to investigate learning and timing of motor responses both in children with ADHD and children with cerebellar lesions. Acquisition, timing and extinction of conditioned eyeblink responses were investigated in children with ADHD, children with chronic surgical cerebellar lesions and controls using a standard delay paradigm with two different interstimulus intervals. Timing of conditioned eyeblink responses was significantly impaired in children with ADHD in the long interstimulus interval condition. Also in children with cerebellar lesions conditioned responses (CR) tended to occur earlier than in controls. Incidences of CRs were significantly reduced in children with cerebellar lesions and tended to be less in children with ADHD than in controls. Extinction of the CRs was impaired in children with cerebellar lesions in both interstimulus interval conditions and in children with ADHD in the long interstimulus interval condition. Cerebellar malfunction may contribute to disordered eyeblink conditioning in ADHD. However, because CR abnormalities differed between ADHD and cerebellar subjects, dysfunction of non-cerebellar structures cannot be excluded.

Short article: Impaired context maintenance in mild to moderately depressed students

We test the hypothesis that people with depression experience difficulties in maintaining task-relevant context information over longer periods of time using the AX version of the continuous performance task (AX-CPT). The AX-CPT requires that participants maintain a context cue (A) in an active state in order to respond correctly to a target cue (X) presented after a short delay. A total of 40 nondepressed and mild to moderately depressed students completed versions of the task with short (1-s) or long (10-s) interstimulus intervals (ISIs). Mildly depressed participants made significantly more context-dependent (BX) errors, unlike controls who made more errors on trials where good context processing would impair performance (AY). This pattern of errors was only evident in the long ISI condition, suggesting poor maintenance of contextual information.

Prestimulus EEG alpha activity reflects temporal expectancy

Since prestimulus EEG alpha activity has recently been considered to convey prestimulus top-down processing, we investigated whether prestimulus alpha activity reflects temporal expectancy of upcoming stimulation even under the non-classical contingent negative variation (CNV) paradigm. EEG was recorded from 16 subjects performing a color and a shape discrimination task manipulated with constant and variable inter-stimulus interval (ISI) conditions. The power of oscillatory activity was investigated by convolving the EEG signals with Morlet wavelets. The constant ISI condition yielded significantly shorter reaction times than the variable ISI condition, indicating more efficient preparation for upcoming stimuli during the constant ISI. We found significantly higher prestimulus alpha activity in the constant ISI condition than in the variable ISI condition, but no significant CNV even in the constant ISI condition. Such a reflection of temporal expectancy in the prestimulus alpha activity corroborates that the prestimulus top-down mental state for preparing upcoming task-performance is considerably reflected in the prestimulus ongoing alpha activity.

Effects of two training procedures in cross-language perception of tones

This study evaluated two perceptual training procedures that might be used to increase native English (NE) and native Chinese (NC) listeners’ ability to discriminate the mid- vs. low-tone contrast in Thai under two inter-stimulus-interval (ISI) conditions (500 and 1500 ms). Participants received training using either a two-alternative forced-choice identification (ID) procedure or a categorial same/different discrimination (SD) procedure. The results obtained indicated that (a) NC listeners outperformed NE listeners both before and after training under both ISI conditions; (b) before training, NC listeners’ discrimination was better under the longer ISI while NE listeners’ performance was comparable across the two ISIs, but no ISI difference was observed for either group of listeners after training; (c) both NE and NC listeners’ performances significantly improved after training, but the improvement was significantly greater among NE listeners under both ISI conditions, and (d), the amount of improvement was comparable across the two training procedures and across the two ISI conditions. These results suggest that both ID and SD training procedures were equally effective in improving NE and NC listeners’ discrimination of the mid- vs. low-tone contrast in Thai and that prior experience with a tone language may prove advantageous in learning another tone language.

The effects of interstimulus interval on event-related indices of attention: An auditory selective attention test of perceptual load theory

ObjectiveWe examined the impact of perceptual load by manipulating interstimulus interval (ISI) in two auditory selective attention studies that varied in the difficulty of the target discrimination. MethodsIn the paradigm, channels were separated by frequency and target/deviant tones were softer in intensity. Three ISI conditions were presented: fast (300ms), medium (600ms) and slow (900ms). Behavioral (accuracy and RT) and electrophysiological measures (Nd, P3b) were observed. ResultsIn both studies, participants evidenced poorer accuracy during the fast ISI condition than the slow suggesting that ISI impacted task difficulty. However, none of the three measures of processing examined, Nd amplitude, P3b amplitude elicited by unattended deviant stimuli, or false alarms to unattended deviants, were impacted by ISI in the manner predicted by perceptual load theory. ConclusionsThe prediction based on perceptual load theory, that there would be more processing of irrelevant stimuli under conditions of low as compared to high perceptual load, was not supported in these auditory studies. SignificanceTask difficulty/perceptual load impacts the processing of irrelevant stimuli in the auditory modality differently than predicted by perceptual load theory, and perhaps differently than in the visual modality.

The effects of very slow rates of stimulus presentation on event-related potential estimates of hearing threshold

The present study evaluated the use of slow rates of stimulus presentation on the accuracy of the N1-P2 cortical response in estimating hearing threshold. Long interstimulus intervals (ISI) allow the non-specific component of the N1 response to emerge, believed to reflect widespread cortical arousal that facilitates sensory and motor responses. We examined whether the non-specific N1 would be elicited at intensity levels near threshold. Event-related potentials were recorded to 0.5-, 1.0, and 4.0-kHz tone bursts with a long ISI (8–12 s) while the eleven subjects read a book. The stimulus level varied from -5 to 45 dB nHL. The 1.0-kHz tone burst was also presented with a shorter ISI (1.5–2.5 s), akin to that typically used in the audiological setting. The amplitude of N1-P2 was significantly enhanced in the long compared to short ISI condition, but, importantly, only for the stimuli with a level ≥25 dB nHL. Therefore, the N1-P2 recorded with long ISIs was not more precise in estimating threshold than that recorded with short ISIs, remaining visible to within 10 dB of behavioural threshold.

A P300 event-related potential brain–computer interface (BCI): The effects of matrix size and inter stimulus interval on performance

We describe a study designed to assess properties of a P300 brain–computer interface (BCI). The BCI presents the user with a matrix containing letters and numbers. The user attends to a character to be communicated and the rows and columns of the matrix briefly intensify. Each time the attended character is intensified it serves as a rare event in an oddball sequence and it elicits a P300 response. The BCI works by detecting which character elicited a P300 response. We manipulated the size of the character matrix (either 3 × 3 or 6 × 6) and the duration of the inter stimulus interval (ISI) between intensifications (either 175 or 350 ms). Online accuracy was highest for the 3 × 3 matrix 175-ms ISI condition, while bit rate was highest for the 6 × 6 matrix 175-ms ISI condition. Average accuracy in the best condition for each subject was 88%. P300 amplitude was significantly greater for the attended stimulus and for the 6 × 6 matrix. This work demonstrates that matrix size and ISI are important variables to consider when optimizing a BCI system for individual users and that a P300-BCI can be used for effective communication.

Spatiotemporal Balance in Competing Apparent Motion is Not Predicted from the Strength of the Single-Motion Percept

Apparent motion is useful for investigating how spatiotemporal cues are integrated to determine the identity of a moving object. To examine its spatiotemporal properties, a competing-motion paradigm has advantages in strict psychophysical evaluation, despite difficulty in object-identity determination, over a non-competing subjective-grading paradigm. The latter has been often used, whereas the former has not been fully investigated. Here, we compared these two paradigms. In the competing-motion experiment, a sample spot was followed by a far and a near test spot with onset asynchrony. We found that the onset asynchrony between the near and far test spots was directly related to the distance ratio between them. This spatial size-invariant relation was not predicted from the strength of the single-apparent-motion percept, estimated from the non-competing subjective-grading experiment in which a sample spot was followed by only one test spot. Moreover, the spatiotemporal balance in competing apparent motion was found not to be valid under negative interstimulus-interval conditions, although a single apparent motion is perceived in those conditions. These clear discrepancies suggest that competing and single apparent motions are processed in a different way according to the difficulty in object identification.

The role of stimulus salience in CPT-AX performance of schizophrenia patients

CPT-AX performance deficit in schizophrenia is well documented but it is unclear what causes this impairment. Past studies have focused on the roles of sustained attention and context processing in CPT-AX but the role of working memory (WM) has not been fully examined even though encoding and maintenance of the cue in WM may be critical to CPT-AX. The major goal of this study was to investigate the effects of stimulus encoding in WM on CPT-AX. Encoding was manipulated by presenting different colored (i.e., salient) cue stimuli on 20% of the trials. WM maintenance was manipulated by varying the cue–target interstimulus interval (ISI). A control task (CPT-Single) that does not require WM but assesses sustained attention was also administered. Schizophrenia patients (SZ) were impaired compared with normal controls (CO) on the CPT-AX overall but not in CPT-Single. For both groups, CPT-AX accuracy improved on salient cue trials in the long ISI condition. In the short ISI condition, where accuracy was already high, the cue saliency effect was observed in the faster RT and SZ benefited significantly more than CO. The effect of target salience was not observed in the CPT-Single, which assesses sustained attention. These results suggest that the facilitation of WM encoding by enhancing cue salience may be a key to improving CPT-AX performance.

Auditory and visual refractory period effects in children and adults: An ERP study

Objective This developmental study was designed to investigate event-related potential (ERP) refractory period effects in the auditory and visual modalities in children and adults and to correlate these electrophysiological measures with standard behavioral measures. Methods ERPs, accuracy, and reaction time were recorded as school-age children and adults monitored a stream of repetitive standard stimuli and detected occasional targets. Standards were presented at various interstimulus intervals (ISIs) in order to measure refractory period effects on early sensory components. Results As has been reported previously in adults, larger components for standards with longer ISIs were observed for an auditory N1 and the visual occipital P1 and P2 in adults. Remarkably similar effects were observed in children. However, only children showed refractory effects on the amplitude of the visual N1 and P2 measured at anterior sites. Across groups, behavioral accuracy and reaction time were correlated with latencies of auditory N1 and visual P2 across ISI conditions. Conclusions The results establish a normal course of development for auditory and visual ERP refractory period effects across the 6- to 8-year-old age range and indicate similar refractoriness in the neural systems indexed by ERPs in these paradigms in typically developing children and adults. Further, the results suggest that electrophysiological measures and standard behavioral measures may at least in part index similar processing in the present paradigms. Significance These findings provide a foundation for further investigation into atypical development, particularly in those populations for which processing time deficits have been implicated such as children with specific language impairment or dyslexia.

Visual event-related potentials under different interstimulus intervals in Parkinson's disease: Relation to motor disability, WAIS-R, and regional cerebral blood flow

We have introduced S1–S2 paradigm (task S) as well as oddball paradigm (task O) visual event-related potentials (ERPs) under different interstimulus intervals (ISIs) in Parkinson's disease (PD). ERP measurements were correlated with motor disability, WAIS-R, and regional cerebral blood flow (rCBF). The ‘group’ influence was characterized by longer latency for P300, N200, and reaction time and decreased P300 amplitude in PD. Both P300 latency and reaction time during task O showed significantly longer latency in longer ISI condition. Our results revealed ‘ISI’ influence on ERPs during task S and significant correlation between ERPs and rCBF in task S.

Selection and inhibition in infancy: evidence from the spatial negative priming paradigm

We used a spatial negative priming (SNP) paradigm to examine visual selective attention in infants and adults using eye movements as the motor selection measure. In SNP, when a previously ignored location becomes the target to be selected, responses to it are impaired, providing a measure of inhibitory selection. Each trial consisted of a prime and a probe, separated by 67, 200, or 550 ms interstimulus intervals (ISIs). In the prime, a target was accompanied by a distractor. In the probe, the target appeared either in the location formerly occupied by the distractor (ignored repetition) or in another location (control). Adults exhibited the SNP effect in all three ISI conditions, producing slower saccade latencies on ignored repetition versus control trials. The SNP effect obtained for infants only under 550 and 200 ms ISI conditions. These results suggest that important developments in visual selection are rooted in emerging inhibitory mechanisms.

Training English and Chinese Listeners to Perceive Thai Tones: A Preliminary Report

The ability of native English (NE) and native Chinese (NC) speakers to identify and discriminate the mid‐ versus the low‐tone contrast in Thai was investigated before and after auditory training. The variables under investigation were first language background and the interstimulus interval (ISI) of the presentation (500 ms vs. 1500 ms). The NC group outperformed the NE group in its ability to discriminate the two Thai tones under the ISI 500 ms condition before training and under both ISI conditions after training. A significant improvement in identification from the pretest to the posttest was observed in the NC group under both ISI conditions, but not in the NE group. These results suggest that prior experience with the tone system in one tone language may be transferable to the perception of tone in another language.

Nonpatient CPT performance varying target frequency and interstimulus interval on five response measures

Studies of sustained attention using the Continuous Performance Test (CPT) often incorporate effortful processing conditions and different response measures. Difficulty of attentional effort and interrelationships among response measures, however, have not been well established particularly with normal populations. This study investigated three CPT tasks which varied in interstimulus interval and target frequency in 107 nonpatient adults. This report also examined five response measures ( d′, a measure of discriminability; In( β), a measure of response bias; reaction time; and omission and commission errors). Findings indicated that a high target frequency condition was more effortful than a short interstimulus interval condition on all response measures. Further, d′, omission errors, and commission errors differentiated the short interstimulus interval condition from baseline, but reaction time and In( β) did not. Participants with faster reaction times in the high target frequency condition had fewer omission errors but more commission errors; these relationships may have been mediated by response bias. This suggested that response measures were interrelated but nonredundant, and that these relationships were influenced by attentional effort and response bias.

Differential modulation of temporal and frontal components of the somatosensory N140 and the effect of interstimulus interval in a selective attention task

The modulation of the somatosensory N140 was examined in a selective attention task where a control condition was applied and the interstimulus interval (ISI) was varied. Electrical stimuli were randomly presented to the left index ( p=0.4) and middle fingers ( p=0.1), and right index ( p=0.4) and middle fingers ( p=0.1). In the attend-right condition, subjects were instructed to count silently the number of infrequent target stimuli presented to the right middle finger, and to the left middle finger in the attend-left condition. They had no task in the control condition. Each condition was performed with two different sets of ISI (mean 400 vs. 800 ms). The somatosensory N140 elicited by frequent standard stimuli was analyzed. The N140 amplitude was larger for the attended ERP compared to the control and unattended ERPs. This attention effect was more marked at the frontal electrodes compared to the temporal electrodes contralateral to the stimulation side. Furthermore, the attention effect at the frontal electrode was larger when the ISI was 800 ms than when it was 400 ms. The N140 amplitude did not differ between the control and unattended ERPs, which might show that a small processing negativity (PN) occurred during the control condition or difference in vigilance level between them. In conclusion, the early lateral (“temporal”) and late midline (“frontal”) components of the N1 (N140) show different behavior, and thus may have different functional significance. Enhancement of the attention effect at the frontal electrode in the longer ISI condition supports the hypothesis that it is related to stronger, voluntary maintenance of the attentional trace.

Older adult performance on an altered version of the SSI test.

The Synthetic Sentence Identification (SSI) test has been used extensively in investigations of reduced speech understanding skills in older adults. In this study the SSI test was altered by adding noise to the competing message and by administering practice lists and equivalent test lists, as well as versions of the test that have 4- and 12-s interstimulus intervals (ISIs), along with the standard 8-s ISI. The purpose was to determine the effect of these alterations on performance in a group of older adults with average pure-tone average 2 values less than 33 dB HL. Performance changed as a function of the ISI, with less rollover occurring for the 4-s ISI condition than the other 2 ISIs.