Effects Of Interstimulus Interval Research Articles

A Simple Computational Model of Semantic Priming in 18-Month-Olds.

We propose a simple computational model that describes potential mechanisms underlying the organization and development of the lexical-semantic system in 18-month-old infants. We focus on two independent aspects: (i) on potential mechanisms underlying the development of taxonomic and associative priming, and (ii) on potential mechanisms underlying the effect of Inter Stimulus Interval on these priming effects. Our model explains taxonomic priming between words by semantic feature overlap, whereas associative priming between words is explained by Hebbian links between semantic representations derived from co-occurrence relations between words (or their referents). From a developmental perspective, any delay in the emergence of taxonomic priming compared to associative priming during infancy seems paradoxical since feature overlap per se need not be learned. We address this paradox in the model by showing that feature overlap itself is an emergent process. The model successfully replicates infant data related to Inter Stimulus Interval effects in priming experiments and makes testablepredictions.

The effect of interstimulus interval on sustained attention

The ability of nervous systems to filter out irrelevant and repetitive stimuli may prevent animals from becoming ‘saturated’ with excess information. However, animals must be particular about which stimuli to attend to and which to ignore, as mistakes may be costly. Using a comparative approach, we explored the effect of interstimulus interval (ISI) between repeated presentations of visual stimuli presented on a screen to test the decrease in responses (response decrement) of both Trite planiceps jumping spiders and untrained Columba livia pigeons, animals with comparable visual ability despite having structurally different visual systems and brain size. We used ISIs of 2.5 s, 5 s, 10 s, predicting that decreases in ISI would lead to progressively less responses to the stimuli. Following from previous work on T. planiceps, we also manipulated pigeon hunger level, finding that hungry birds were initially more responsive than sated pigeons, but the rate of decrease in responses to the stimulus did not differ between the two groups. While a clear response decrement was seen in both species across all conditions, shorter ISIs resulted in more dramatic response decrements, aligning with previous work and with the resource depletion theory posited in the human-based literature.

Effects of inter-stimulus and inter-trial intervals on somatosensory gating

Aim of the study Sensory gating is a human higher cognitive function that serves to suppress excessive sensory information and prevent brain overactivity. To elucidate this function, a paired-pulse stimulation paradigm has been used while recording electroencephalography (EEG), and evaluated as an amplitude ratio of responses to a second stimulus (S2) over responses to the first stimulus (S1). The present study investigated the effects of the inter-stimulus interval (ISI) and inter-trial interval (ITI) on somatosensory gating using somatosensory-evoked potentials (SEPs). Methods In Experiment 1, ISI was set at five conditions: 200, 400, 600, 800, and 1000 ms. In Experiment 2, ITI was set at four conditions: 1, 2, 4, and 8 s. Results ISI affected the S2/S1 amplitude ratios of P22 and N27 at C3’ and N30 at Fz, and these S2/S1 amplitude ratios decreased the most under the 200 and 400-ms conditions. ITI affected the S2/S1 amplitude ratios of P22, N27, and N60 at C3', and especially, the somatosensory gating did not work under the 1-s condition. These results suggest that not all SEP components are modulated in the same manner with changing ISI and ITI. The effects of ISI and ITI independently affected the somatosensory gating. Conclusions Based on our findings, preferable parameters are 200-400 ms for ISI and 4 s or longer for ITI to evaluate the functional mechanisms on somatosensory gating in SEPs.

Neural Network Circuits for Bionic Associative Memory and Temporal Order Memory Based on DNA Strand Displacement.

Pavlovian associative memory plays an important role in our daily life and work. The realization of Pavlovian associative memory at the deoxyribonucleic acid (DNA) molecular level will promote the development of biological computing and broaden the application scenarios of neural networks. In this article, bionic associative memory and temporal order memory circuits are constructed by DNA strand displacement (DSD) reactions. First, a temporal logic gate is constructed on the basis of DSD circuit and extended to a three-input temporal logic gate. The output of temporal logic gate is used for the weight species of associative memory. Second, the forgetting module and output module based on the DSD circuit are constructed to realize some functions of associative memory, including associative memory with simultaneous stimulus, associative memory with interstimulus interval effect, and the facilitation by intermittent stimulus. In addition, the coding, storage, and retrieval modules are designed based on the analysis and memory capabilities of temporal logic gate for temporal information. The temporal order memory circuit is constructed, demonstrating the temporal order memory ability of DNA circuit. Finally, the reliability of the circuit is verified through Visual DSD software simulation. Our work provides ideas and inspiration to construct more complex DNA bionic circuits and intelligent circuits by using DSD technology.

Design and Implementation of Pavlovian Associative Memory Based on DNA Neurons.

In the field of biocomputing and neural networks, deoxyribonucleic acid (DNA) strand displacement (DSD) technology performs well in computation, programming, and information processing. In this article, the multiplication gate, addition gate, and threshold gate based on DSD are used to cascade into a single DNA neuron. Multiple DNA neurons can be cascaded to form different neural networks. The DNA neural networks are designed to implement seven classical conditioned reflexes from Pavlovian associative memory experiments. A classical conditioned reflex is a combination of a conditioned stimulus (CS) and another un CS with a reward or punishment. So that the individual develops a conditioned reflex that is similar to an unconditioned reflex in the use of CS alone. The seven classical conditioned reflexes include acquisition and forgetting, interstimulus interval effect, blocking, conditioned inhibition, overshadowing, generation, and differentiation. The simulations are verified by the software visual DSD. This article provides a direction for the integration of biology and psychology.

Contributed Session II: The relationship between temporal summation at detection threshold and fixational eye movements.

We studied the relationship between the threshold temporal summation of increment pulses and fixational eye-movements. Six participants completed a 2AFC increment detection task. Stimuli were 0.16 x 2.2 arcmin increments of 543 nm light presented via an AOSLO with a 60 Hz frame rate. Stimuli for temporal integration were two single frame presentations with a 16 ms (consecutive frames), 33 ms, 100 ms, or 300 ms inter-stimulus interval (ISI). Data were also collected for increments presented on a single frame. Stimuli were presented in either world-fixed coordinates (natural retinal image motion) or were stabilised on the retina. There were large differences in overall sensitivity across individuals, but the time-course of performance change with ISI was similar across participants. Thresholds for ISI=33 ms were close to performance with two consecutive frames, suggesting complete summation of light energy; whereas thresholds for ISI=300 ms were closer to the single-frame case, suggesting limited summation; and thresholds for ISI=100 ms were intermediate, suggesting residual summation. The effect of ISI on threshold was similar for stabilised stimuli and natural viewing, but there was a small trend towards lower thresholds for stabilised stimuli at short ISI and vice-versa at long ISI. We plan to present our results in the context of an ideal observer calculation that may clarify how the initial visual encoding, including temporal summation within cones, shapes performance.

Effects of interstimulus interval and significance on electrodermal and central measures of the phasic orienting reflex (OR) in a dishabituation task

Although the P300 event-related potential (ERP) is the most likely central measure of Sokolov’s Orienting Reflex (OR), there are few systematic comparisons with the skin conductance response (SCR), the “gold standard” electrodermal OR measure. We examine habituation, stimulus significance, and inter-stimulus interval (ISI) effects in SCRs and components of the P300 from single-trial ERPs in an auditory dishabituation paradigm. Single trial ERP components were separated by temporal principal components analysis, and five components of the P300 were examined as potential phasic OR measures: P3a, P3b, Novelty P3, and two Slow Waves (SW1, SW2). Across the factors of ISI and significance, SCRs showed decrement over trials, recovery at a deviant, and dishabituation at the subsequent standard. This general pattern was not present in any of the components of the P300. SCRs were also larger to significant stimuli and at the long ISI; effects differed between P300 components. The electrodermal SCR showed the complete profile over trials expected of the phasic OR, and was enhanced by stimulus significance, confirming it as the model measure of Sokolov’s phasic OR. Components of the P300 failed to match this profile, but instead appear to reflect different aspects of the stimulus processing involved in OR elicitation.

Intensity and inter-stimulus-interval effects on human middle- and long-latency auditory evoked potentials in an unpredictable auditory context.

It is not known how Auditory-Evoked Responses (AERs) comprising Middle Latency Responses (MLRs) and Long Latency Responses (LLRs) are modulated by stimulus intensity and inter-stimulus interval (ISI) in an unpredictable auditory context. Further, intensity and ISI effects on MLR and LLR have never been assessed simultaneously in the same humans. To address this important question, thirty participants passively listened to a random sequence of auditory clicks of three possible intensities (65, 75, and 85 dB) at five possible ISI ranges (0.25 to 0.5s, 0.5 to 1s, 1 to 2s, 2 to 4s, 4 to 8s) over four to seven one-hour sessions while EEG was recorded. P0, Na, Pa, Nb, and Pb MLR peaks and N1 and P2 LLR peaks were measured. MLRs P0 (p=.005), Pa (p=.021), and Pb (p=<.001) were modulated by intensity, while only MLR Pb (p=<.001) was modulated by ISI. LLR N1 and P2 were modulated by both intensity and ISI (all p values < .001). Intensity and ISI interacted at Pb, N1, and P2 (all p values < .001), with greater intensity effects at longer ISIs and greater ISI effects at louder intensities. Together, these results provide a comprehensive picture of intensity and ISI effects on AER across the entire thalamocortical auditory pathway, while controlling for stimulus predictability. Moreover, they highlight P0 as the earliest MLR response sensitive to stimulus intensity and Pb (~50 ms) as the earliest cortical response coding for ISIs above 250 ms and showing an interdependence between intensity and ISI effects.

A full-function memristive pavlov associative memory circuit with inter-stimulus interval effect

Time interval between stimuli plays a critical role in Pavlov classical conditioning. In this paper, a full-functional memristive Pavlov associative memory circuit with inter-stimulus interval effect is proposed. Compared with previous works, the proposed circuit extends the Pavlov associative memory with time interval to three complex situations of conditioning and realizes bionic associative memory learning curves called inter-stimulus interval effect. On this basis, the phenomena related to time interval in classical conditioning, blocking and facilitation, are implemented. PSPICE is used to simulate the whole circuit, and the simulation results demonstrate above functions. Furthermore, an application on classification is extended on the basis of the proposed circuit. The application circuit is also verified by the simulation results in PSPICE. This paper provides a reference to associative memory based on memristor in complex time situations.

Time Delay Affects Thermal Discrimination.

Time order errors have been investigated in several fields, and the time delay between subsequent stimuli in discrimination tasks is one example of such errors. However, the effect of these types of errors in thermal discrimination tasks is understudied. To evaluate the effect of inter-stimulus interval (ISI) on thermal perception, we used a discrimination task with a staircase method between two non-zero thermal stimuli. We found that JND ISI=0s was 3.10 and increased by 11.9% and 21.2% at JND ISI=3s and JND ISI=9s, respectively. Statistical analysis revealed that ISI was a statistically significant effect ( ) on thermal perception in our task. Future studies on thermal perception should keep the ISI consistent and report the time.

Effects of inter-stimulus intervals on concurrent P300 and SSVEP features for hybrid brain-computer interfaces

BackgroundRecently, we have implemented a high-speed brain-computer interface (BCI) system with a large instruction set using the concurrent P300 and steady-state visual evoked potential (SSVEP) features (also known as hybrid features). However, it remains unclear how to select inter-stimulus interval (ISI) for the proposed BCI system to balance the encoding efficiency and decoding performance. New methodThis study developed a 6 * 9 hybrid P300-SSVEP BCI system and investigated a series of ISIs ranged from −175–0 ms with a step of 25 ms. The influence of ISI on the hybrid features was analyzed from several aspects, including the amplitude of the induced features, classification accuracy, information transfer rate (ITR). Twelve naive subjects were recruited for the experiment. ResultsThe results showed the ISI factor had a significant impact on the hybrid features. Specifically, as the values of ISI decreased, the amplitudes of the induced features and accuracies decreased gradually, while the ITRs increased rapidly. It’s achieved the highest ITR of 158.50 bits/min when ISI equal to − 175 ms. Comparison with Existing MethodThe optimal ISI in this study achieved superior performance in comparison with the one we used in the previous study. ConclusionsThe ISI can exert an important influence on the P300-SSVEP BCI system and its optimal value is − 175 ms in this study, which is significant for developing the high-speed BCI system with larger instruction sets in the future.

Temporal Profile of Descending Cortical Modulation of Spinal Excitability: Group and Individual-Specific Effects.

Sensorimotor control is modulated through complex interactions between descending corticomotor pathways and ascending sensory inputs. Pairing sub-threshold transcranial magnetic stimulation (TMS) with peripheral nerve stimulation (PNS) modulates the Hoffmann’s reflex (H-reflex), providing a neurophysiologic probe into the influence of descending cortical drive on spinal segmental circuits. However, individual variability in the timing and magnitude of H-reflex modulation is poorly understood. Here, we varied the inter-stimulus interval (ISI) between TMS and PNS to systematically manipulate the relative timing of convergence of descending TMS-induced volleys with respect to ascending PNS-induced afferent volleys in the spinal cord to: (1) characterize effective connectivity between the primary motor cortex (M1) and spinal circuits, mediated by both direct, fastest-conducting, and indirect, slower-conducting descending pathways; and (2) compare the effect of individual-specific vs. standard ISIs. Unconditioned and TMS-conditioned H-reflexes (24 different ISIs ranging from −6 to 12 ms) were recorded from the soleus muscle in 10 able-bodied individuals. The magnitude of H-reflex modulation at individualized ISIs (earliest facilitation delay or EFD and individual-specific peak facilitation) was compared with standard ISIs. Our results revealed a significant effect of ISI on H-reflex modulation. ISIs eliciting earliest-onset facilitation (EFD 0 ms) ranged from −3 to −5 ms across individuals. No difference in the magnitude of facilitation was observed at EFD 0 ms vs. a standardized short-interval ISI of −1.5 ms. Peak facilitation occurred at longer ISIs, ranging from +3 to +11 ms. The magnitude of H-reflex facilitation derived using an individual-specific peak facilitation was significantly larger than facilitation observed at a standardized longer-interval ISI of +10 ms. Our results suggest that unique insights can be provided with individual-specific measures of top-down effective connectivity mediated by direct and/or fastest-conducting pathways (indicated by the magnitude of facilitation observed at EFD 0 ms) and other descending pathways that encompass relatively slower and/or indirect connections from M1 to spinal circuits (indicated by peak facilitation and facilitation at longer ISIs). By comprehensively characterizing the temporal profile and inter-individual variability of descending modulation of spinal reflexes, our findings provide methodological guidelines and normative reference values to inform future studies on neurophysiological correlates of the complex array of descending neural connections between M1 and spinal circuits.

NEUOPHYSIOLOGICAL CHANGES AFTER UPPER AND LOWER LIMB GRADED EXERCISE TESTING.

Aerobic exercise, including graded exercise testing (GXT), may cause neurophysiological changes of circuits in the primary motor cortex (M1) related to mechanisms of fatigue and/or plasticity. Investigating M1 inhibitory circuit changes over time in exercising compared to non-exercising muscles after GXT of the upper limbs (UL) and lower limbs (LL) may distinguish between different post-exercise mechanisms. PURPOSE: To evaluate M1 inhibitory circuit changes resulting from UL and LL GXT and determine their associations with fitness. METHODS: Six healthy subjects (30 ± 6 yrs) participated. Transcranial Magnetic Stimulation (TMS), Peripheral Nerve Stimulation (PNS), and Electromyography (EMG) were used for neurophysiological testing. Gas analysis was performed to evaluate VO2max (UL: 24.2 ± 4.8, LL: 35.1 ± 5.9 mL/kg/min) during GXTs. Surface electrodes were placed over the first dorsal interosseous (FDI) and tibialis anterior (TA) muscles. Measures of M1 and M1-related afferent inhibition included cortical silent period (CSP) and short-latency afferent inhibition (SAI), respectively. SAI inter-stimulus intervals (ISI) between PNS and TMS stimulations were 21-23ms (UL), and 32-35ms (LL). TMS coil orientation (CO) was altered between posterior-anterior (PA) and anterior-posterior (AP) for both measures of CSP and SAI. CSP and SAI were taken 0-45 min (POST1) and 45-90 min (POST2) post-exercise and compared to pre-exercise. Repeated measures ANOVAs were performed to evaluate effects of exercise type, CO, time, and ISI. RESULTS: CSP decreased at POST1 and increased at POST2 in FDI (97.9 ± 1.2% vs. 104.5 ± 2.5%, p < 0.05) with a trend toward significance in TA (99.3 ± 2.5% vs. 103.5 ± 4.9%, p = 0.19). Although SAI was found for the TA at 32ms (p<0.05) and FDI at 21-23ms (p < 0.05), the interaction of exercise type, CO, and ISI did not reach significance after Huynh-Feldt correction (FDI: p = 0.10, TA: p = 0.10). Univariate linear regression of VO2max and SAI revealed a potential relationship reliant on exercise type and CO (UL: R2 = 0.91, LL: R2 = 0.68). CONCLUSIONS: Changes in CSP suggest that exercise may cause early disinhibition followed by greater inhibition in M1 while changes in SAI may be influenced by fitness levels. Collectively, the results support UL and LL GXTs cause measurable M1 neurophysiological changes.

Lowered Rhythm Tapping Ability in Patients With Constructional Apraxia After Stroke.

Rhythm tapping tasks are often used to explore temporal reproduction abilities. Many studies utilizing rhythm tapping tasks are conducted to evaluate temporal processing abilities with neurological impairments and neurodegenerative disorders. Among sensorimotor and cognitive disorders, rhythm processing abilities in constructional apraxia, a deficit in achieving visuospatial constructional activities, has not been evaluated. This study aimed to examine the rhythm tapping ability of patients with constructional apraxia after a stroke. Twenty-four patients were divided into two groups: with and without constructional apraxia. There were 11 participants in the constructional apraxia group and 13 in the without constructional apraxia group. The synchronization-continuation paradigm was employed in which a person performs a synchronized tapping activity to a metronome beat and continues tapping after the beat has stopped. For statistical analysis, a three-way mixed analysis of variance (2 × 2 × 3) was conducted. The factors were groups (with and without constructional apraxia), tapping tasks (synchronization and continuation), and inter-stimulus intervals (600, 750, and 1000 ms). A significant effect of group factor was found (F[1,132] = 16.62; p < 0.001). Patients in the without constructional apraxia group were able to more accurately reproduce intervals than those in the constructional apraxia group. Moreover, a significant effect of tapping tasks was found (F[1,132] = 8.22; p < 0.01). Intervals were reproduced more accurately for synchronization tasks than continuation tasks. There was no significant inter-stimulus interval effect. Overall, these results suggest that there might be a relation between temporal and spatial reproductions in a wide spectrum of processing levels, from sensory perception to cognitive function.

Cerebellar Transcranial Magnetic Stimulation Reduces the Silent Period on Hand Muscle Electromyography During Force Control.

This study aimed to investigate whether cerebellar transcranial magnetic stimulation (C-TMS) affected the cortical silent period (cSP) induced by TMS over the primary motor cortex (M1) and the effect of interstimulus interval (ISI) on cerebellar conditioning and TMS to the left M1 (M1-TMS). Fourteen healthy adult participants were instructed to control the abduction force of the right index finger to 20% of the maximum voluntary contraction. M1-TMS was delivered during this to induce cSP on electromyograph of the right first dorsal interosseous muscle. TMS over the right cerebellum (C-TMS) was conducted prior to M1-TMS. In the first experiment, M1-TMS intensity was set to 1 or 1.3 × resting motor threshold (rMT) with 20-ms ISI. In the second experiment, the intensity was set to 1 × rMT with ISI of 0, 10, 20, 30, 40, 50, 60, 70, or 80 ms, and no-C-TMS trials were inserted. In results, cSP was significantly shorter in 1 × rMT condition than in 1.3 × rMT by C-TMS, and cSP was significantly shorter for ISI of 20–40 ms than for the no-C-TMS condition. Further, motor evoked potential for ISI40-60 ms were significantly reduced than that for ISI0. Thus, C-TMS may reduce cSP induced by M1-TMS with ISI of 20–40 ms.

Specific inter-stimulus interval effect of NMDA receptor activation in the insular cortex during conditioned taste aversion.

Taste memory recognition is crucial for species survival; thus, the acquisition of conditioned taste aversion (CTA) protects animals against consuming poisons or toxins. In nature, food and poison are confined in the same edible item; however, in the laboratory these food constituents are usually presented separately for experimental analysis. The taste, or conditioned stimulus (CS), can be hours apart from the gastric malaise, or unconditioned stimulus (US); this extended inter-stimulus interval (ISI) allows the analysis of a particular learning phase. Evidence indicates a relevant function of glutamatergic activity in the insular cortex (IC) throughout the ISI. N-methyl-D-aspartate receptors (NMDAR) are crucial during CTA acquisition and retrieval. However, the exact participation of NMDAR in the IC during the ISI has not been demonstrated. Thus, the aim of this work was to evaluate the effects of temporal NMDAR activation during four time frames throughout the ISI of conditioned sugar aversion with bilateral injections of NMDA at a physiological dose (1 µg/µl) in the IC, given (1) immediately before or (2) immediately after sugar presentation, or (3) immediately before or (4) immediately after LiCl i.p. injection. The results showed that NMDAR activation in the IC had a specific ISI effect during CTA acquisition, increasing aversive memory formation and delaying extinction only after CS presentation. Overall, these results demonstrate that NMDAR in the IC have a particular enhancing associative effect after CS and suggest that there is a precise coincidence in neurochemical events in the IC that correlates with the stimulus to be associated and the glutamate NMDAR activity that must be finely tuned in the ISI during CTA acquisition.

Inter-stimulus Interval Effect on Tactile Habituation: An Electrophysiological Approach

Objective: The current study aims to investigate different inter-stimulus interval effect on habituation process by using non-painful tactile stimuli. Methods: Twelve right-handed healthy volunteers (6 female; mean age: 22.9 ± 1.93 years) participated to the study. The electroencephalography (EEG) was recorded from 64 channels. Non-painful tactile stimuli (~140 kPa) were delivered to the right index finger via using a pneumatic stimulator. Somatosensory evoked potentials (SEP) paradigm was used in all session. Inter-stimulus interval (ISI) was selected as 2s, 4s, and 8s and applied in separate sessions (as ISI2, ISI4 and ISI8). Results: Peak-to-peak maximum amplitudes of N2, P3 and N4 components were measured for three different ISI and for three different electrode sites (Fz, Cz, Pz). The 3x3 repeated measures ANOVA test was employed for statistical analysis. According to the analysis, a significant inter-stimulus interval (ISI) effect was found on both PPmaxN2P3 and PPmaxP3N4 (p=0.004 and p=0.001 respectively). The amplitudes of ISI8 session in all electrode sites higher than ISI2 session for both PPmaxN2P3 (p=0.024) and PPmaxP3N4 (p=0.012). Also, ISI4 session has higher amplitudes than ISI2 session (p=0.05) for the PPmaxP3N4. Conclusion: This study revealed that the late components of SEPs are affected by the ISI change. The amplitudes of SEP components are increased as ISI increased.

No trace of phase: Corticomotor excitability is not tuned by phase of pericentral mu-rhythm

BackgroundThe motor potentials evoked by transcranial magnetic stimulation (TMS) over the motor hand area (M1-HAND) show substantial inter-trial variability. Pericentral mu-rhythm oscillations, might contribute to inter-trial variability. Recent studies targeting mu-activity based on real-time electroencephalography (EEG) reported an influence of mu-power and mu-phase on the amplitude of motor evoked potentials (MEPs) in a preselected group with strong pericentral mu-activity. Other studies that determined mu-power or mu-phase based on post-hoc trial sorting according in non-preselected individuals were largely negative. ObjectivesTo reassess if cortico-spinal activity is modulated by the mu-rhythm, we applied single-pulse TMS to the M1-HAND conditional on the phase of the intrinsically expressed pericentral mu-rhythm in 14 non-preselected healthy young participants. MethodsTMS was given at 0, 90, 180, and 270° of the mu-phase. Based on the absence of effects of mu-phase or mu-power when analyzing the mean MEP amplitudes, we also computed a linear mixed effects model, which included mu-phase, mu-power, inter-stimulus interval (ISIs) as fixed effects, treating the subject factor as a random effect. ResultsMixed model analysis revealed a significant effect of mu-power and ISI, but no effect of mu-phase and no interactions. MEP amplitude scaled linearly with lower mu-power or longer ISIs, but these modulatory effects were very small relative to inter-trial MEP variability. ConclusionOur largely negative results are in agreement with previous offline TMS-EEG studies and point to a possible influence of ISI. Future research needs to clarify under which circumstances the responsiveness of human the M1-HAND to TMS depends on the synchronicity with mu-power and mu-phase.

No Effect of Interstimulus Interval on Acoustic Reflex Thresholds.

The acoustic reflex (AR), a longstanding component of the audiological test battery, has received renewed attention in the context of noise-induced cochlear synaptopathy—the destruction of synapses between inner hair cells and auditory nerve fibers. Noninvasive proxy measures of synaptopathy are widely sought, and AR thresholds (ARTs) correlate closely with synaptic survival in rodents. However, measurement in humans at high stimulus frequencies—likely important when testing for noise-induced pathology—can be challenging; reflexes at 4 kHz are frequently absent or occur only at high stimulus levels, even in young people with clinically normal audiograms. This phenomenon may partly reflect differences across stimulus frequency in the temporal characteristics of the response; later onset of the response, earlier onset of adaptation, and higher rate of adaptation have been observed at 4 kHz than at 1 kHz. One temporal aspect of the response that has received little attention is the interstimulus interval (ISI); inadequate duration of ISI might lead to incomplete recovery of the response between successive presentations and consequent response fatigue. This research aimed to test for effects of ISI on ARTs in normally hearing young humans, measured at 1 and 4 kHz. Contrary to our hypotheses, increasing ISIs from 2.5 to 8.5 s did not reduce ART level, nor raise ART reliability. Results confirm that clinically measured ARTs—including those at 4 kHz—can exhibit excellent reliability and that relatively short (2.5 s) ISIs are adequate for the measurement of sensitive and reliable ARTs.

The effect of stimulus encounter rate on response decrement in jumping spiders

The inability to maintain signal detection performance with time on task, or response decrement, has been widely studied. In animals with small brains, the ability to filter out repetitive, irrelevant stimuli may prevent the nervous system from being saturated with information. However, animals must be particular to which stimuli they attend and those to ignore, as mistakes may be costly. We explored the effect of inter-stimulus interval (ISI) between repeated presentations of a visual stimulus on the response decrement of the jumping spider Trite planiceps. Jumping spiders are active visual hunters, and moving visual stimuli trigger a readily observable optomotor response. We used either an ISI of 10 or 20 s between 160 stimulus presentations, predicting that a shorter ISI would result in a steeper decrement through cognitive overstimulation, according to the resource depletion theory. While a clear response decrement was seen for both conditions, the shorter ISI resulted in a more dramatic response decrement, aligning with the resource depletion theory posited in the human-based literature.