Increasing Stimulus Duration Research Articles

On the Effect of High Stimulation Rates on Temporal Loudness Integration in Cochlear Implant Users.

Long stimuli have lower detection thresholds or are perceived louder than short stimuli with the same intensity, an effect known as temporal loudness integration (TLI). In electric hearing, TLI for pulse trains with a fixed rate but varying number of pulses, i.e. stimulus duration, has mainly been investigated at clinically used stimulation rates. To study the effect of an overall effective stimulation rate at 100% channel crosstalk, we investigated TLI with (a) a clinically used single-channel stimulation rate of 1,500 pps and (b) a high stimulation rate of 18,000 pps, both for an apical and a basal electrode. Thresholds (THR), a line of equal loudness (BAL), and maximum acceptable levels (MALs) were measured in 10 MED-EL cochlear implant users. Stimulus durations varied from a single pulse to 300 ms long pulse trains. At 18,000 pps, the dynamic range (DR) increased by dB for the 300 ms pulse train. Amplitudes at THR, BAL, and MAL decreased monotonically with increasing stimulus duration. The decline was fitted with high accuracy with a power law function (). Threshold slopes were and dB per doubling of duration for the low and high rate, respectively, and were shallower than for acoustic hearing. The electrode location did not affect the amplitudes or slopes of the TLI curves. THR, BAL, and MAL were always lower for the higher rate and the DR was larger at the higher rate at all measured durations.

Temporal and spatial summation of laser heat stimuli in cultured nociceptive neurons of the rat

We studied the efficacy of a near-infrared laser (1475 nm) to activate rat dorsal root ganglion (DRG) neurons with short punctate radiant heat pulses (55 µm diameter) and investigated temporal and spatial summation properties for the transduction process for noxious heat at a subcellular level. Strength-duration curves (10–80 ms range) indicated a minimum power of 30.2mW for the induction of laser-induced calcium transients and a chronaxia of 13.9 ms. However, threshold energy increased with increasing stimulus duration suggesting substantial radial cooling of the laser spot. Increasing stimulus duration demonstrated suprathreshold intensity coding of calcium transients with less than linear gains (Stevens exponents 0.29/35mW, 0.38/60mW, 0.46/70mW). The competitive TRPV1 antagonist capsazepine blocked responses to short near-threshold stimuli and significantly reduced responses to longer duration suprathreshold heat. Heating 1/3 of the soma of a neuron was sufficient to induce calcium transients significantly above baseline (p < 0.05), but maximum amplitude was only achieved by centering the laser over the entire neuron. Heat-induced calcium increase was highest in heated cell parts but rapidly reached unstimulated areas reminiscent of spreading depolarization and opening of voltage-gated calcium channels. Full intracellular equilibrium took about 3 s, consistent with a diffusion process. In summary, we investigated transduction mechanisms for noxious laser heat pulses in native sensory neurons at milliseconds temporal and subcellular spatial resolution and characterized strength duration properties, intensity coding, and spatial summation within single neurons. Thermal excitation of parts of a nociceptor spread via both membrane depolarization and intracellular calcium diffusion.

Eliciting neural mechanisms of music medicine for epilepsy

ABSTRACT Prior research involving persons with drug-resistant epilepsy has demonstrated that listening to some music decreases the probability of clinical seizures and their related comorbidities. This article reviews recent research designed to elicit the neural mechanisms behind positive outcomes on biomarkers of the disease. Using novel music analytical and neurophysiological experimental methods, our results showed positive effects on epilepsy using 15-second gamma-band (40-Hz) complex tones as well as Mozart's Sonata for Two Pianos in D Major (K448). We also observed greater effects with increased stimulus duration. Further analysis elicited effects localized to bilateral frontal brain regions due to transitions between musical phrases. Finally, music matched for patient preference from a range of musical styles was not as effective as 40-Hz tones or Mozart's K448. Understanding these results required expertise in both music and neuroscience, and could yield reliable music-based interventions for epilepsy that may also be transferable to other brain disorders.

Contributed Session III: The benefits of naturally moving over stabilized stimuli for acuity increase with longer presentation times

Longer stimulus durations aid in resolving fine spatial detail (Graham & Cook, 1937) - an effect partially attributed to fixational eye movements (FEM; Rucci et al., 2007, Anderson et al., 2020). While FEM do not appear to impact acuity at short presentations (6-300 ms; Tulunay-Keesey & Jones, 1976), recent work has shown that stabilizing stimuli on the retina, eliminating the effects of FEM, impedes acuity at longer durations (750 ms; Ratnam et al., 2017). At intermediate durations, the interplay between acuity and stimulus motion on the retina is not well understood. We used an adaptive optics scanning laser ophthalmoscope to stabilize stimuli on the retina at 1 degree from fixation. A 4 AFC tumbling E staircase was used to find the minimum angle of resolution (MAR) for 100, 375 and 750 ms presentations of unstabilized stimuli. The MAR-duration relationship followed an asymptotic shape, improving from 100 ms (mean MAR ± SEM: 1.84 ± 0.17 arcmin) to 375 ms (1.45 ± 0.09) but not to 750 ms (1.48 ± 0.08). Next, performance (% correct) on stabilized and unstabilized stimuli was measured at each duration's MAR. For stabilized stimuli, we measured performance as a ratio relative to unstabilized performance and found that it degraded with increasing stimulus duration (1.1 ± 0.01, 0.91 ± 0.07, 0.65 ± 0.11 for 100, 375, and 750 ms durations, respectively). These results suggest that retinal stabilization may disrupt the mechanisms by which integration over time enhances visual acuity.

Categorical Perception of Mandarin Pitch Directions by Cantonese-Speaking Musicians and Non-musicians.

Purpose: This study is to investigate whether Cantonese-speaking musicians may show stronger CP than Cantonese-speaking non-musicians in perceiving pitch directions generated based on Mandarin tones. It also aims to examine whether musicians may be more effective in processing stimuli and more sensitive to subtle differences caused by vowel quality.Methods: Cantonese-speaking musicians and non-musicians performed a categorical identification and a discrimination task on rising and falling continua of fundamental frequency generated based on Mandarin level, rising and falling tones on two vowels with nine duration values.Results: Cantonese-speaking musicians exhibited a stronger categorical perception (CP) of pitch contours than non-musicians based on the identification and discrimination tasks. Compared to non-musicians, musicians were also more sensitive to the change of stimulus duration and to the intrinsic F0 in pitch perception in pitch processing.Conclusion: The CP was strengthened due to musical experience and musicians benefited more from increased stimulus duration and were more efficient in pitch processing. Musicians might be able to better use the extra time to form an auditory representation with more acoustic details. Even with more efficiency in pitch processing, musicians' ability to detect subtle pitch changes caused by intrinsic F0 was not undermined, which is likely due to their superior ability to process temporal information. These results thus suggest musicians may have a great advantage in learning tones of a second language.

Neocortical substrates of feelings evoked with music in the ACC, insula, and somatosensory cortex

Neurobiological models of emotion focus traditionally on limbic/paralimbic regions as neural substrates of emotion generation, and insular cortex (in conjunction with isocortical anterior cingulate cortex, ACC) as the neural substrate of feelings. An emerging view, however, highlights the importance of isocortical regions beyond insula and ACC for the subjective feeling of emotions. We used music to evoke feelings of joy and fear, and multivariate pattern analysis (MVPA) to decode representations of feeling states in functional magnetic resonance (fMRI) data of n = 24 participants. Most of the brain regions providing information about feeling representations were neocortical regions. These included, in addition to granular insula and cingulate cortex, primary and secondary somatosensory cortex, premotor cortex, frontal operculum, and auditory cortex. The multivoxel activity patterns corresponding to feeling representations emerged within a few seconds, gained in strength with increasing stimulus duration, and replicated results of a hypothesis-generating decoding analysis from an independent experiment. Our results indicate that several neocortical regions (including insula, cingulate, somatosensory and premotor cortices) are important for the generation and modulation of feeling states. We propose that secondary somatosensory cortex, which covers the parietal operculum and encroaches on the posterior insula, is of particular importance for the encoding of emotion percepts, i.e., preverbal representations of subjective feeling.

Offset analgesia is reduced on the palm and increases with stimulus duration.

A noxious stimulus following a more intense stimulus often feels less painful than continuous noxious stimulation. This effect, known as offset analgesia (OA), may be due to descending inhibitory control, to changes in peripheral neural transmission or both. The timing and location of noxious thermal stimulation were manipulated to better understand the peripheral and central contributions to OA. In a first experiment, participants (n=29) provided continuous pain ratings as stimuli were delivered to the palm or dorsum of each hand. Offset trials included 44°C (T1), 45°C (T2) and 44°C (T3) stimulation periods. Baseline trials were identical except the T3 temperature fell to 35°C. Constant trials were 44°C throughout. The duration of T1 and T2 was either 1s or 6s, whereas T3 was always 12s. In a second experiment, participants (n=43) rated pain levels of noxious stimuli presented to the forearms with varying T1 and T2 durations (3, 6, 10 or 13s) and a 20s T3 period. OA effects became stronger with increasing inducing durations. OA, however, was not found on the palm even at longer durations. The increase in OA with duration suggests that accumulated nociceptive signalling is more important to triggering OA than is a decrease in nociceptors' instantaneous firing rates. The lack of OA on the palm, however, implies a key role for the rapidly adapting Type II AMH fibres that may be absent or not readily activated on the palm. Unravelling the relative central and peripheral contribution to OA requires further investigation. Offset analgesia (OA) is a fundamentally temporal phenomenon dependent on dynamic changes in stimulus intensity. Here we demonstrate increased OA with increased stimulus duration. This finding implies the more slowly-responding AMH-I peripheral mechanoreceptors contribute to OA. The more rapidly responding AMH-II peripheral mechanoreceptors, however, may be absent or more difficult to activate in the palm where we did not observe OA. This finding implies that the AMH-II receptors are necessary for OA. Our studies suggest methods to unravel the different peripheral and central contributions to OA.

Hemodynamic response varies across tactile stimuli with different temporal structures.

Tactile stimuli can be distinguished based on their temporal features (e.g., duration, local frequency, and number of pulses), which are fundamental for vibrotactile frequency perception. Characterizing how the hemodynamic response changes in shape across experimental conditions is important for designing and interpreting fMRI studies on tactile information processing. In this study, we focused on periodic tactile stimuli with different temporal structures and explored the hemodynamic response function (HRF) induced by these stimuli. We found that HRFs were stimulus‐dependent in tactile‐related brain areas. Continuous stimuli induced a greater area of activation and a stronger and narrower hemodynamic response than intermittent stimuli with the same duration. The magnitude of the HRF increased with increasing stimulus duration. By normalizing the characteristics into topographic matrix, nonlinearity was obvious. These results suggested that stimulation patterns and duration within a cycle may be key characters for distinguishing different stimuli. We conclude that different temporal structures of tactile stimuli induced different HRFs, which are essential for vibrotactile perception and should be considered in fMRI experimental designs and analyses.

How musical experience affects tone perception efficiency by musicians of tonal and non-tonal speakers?

PurposeTo investigate if, regardless of language background (tonal or non-tonal), musicians may show stronger CP than non-musicians; To examine if native speakers of English (English or non-tonal musicians henceforth) or Mandarin Chinese (Mandarin or tonal musicians henceforth) can better accommodate multiple functions of the same acoustic cue and if musicians’ sensitivity to pitch of lexical tones comes at the cost of slower processing.MethodEnglish and Mandarin Musicians and non-musicians performed a categorical identification and a discrimination task on rising and falling continua of fundamental frequency on two vowels with 9 duration values.ResultsNon-tonal musicians exhibited significantly stronger categorical perception of pitch contour than non-tonal non-musicians. However, tonal musicians did not consistently perceive the two types of pitch directions more categorically than tonal non-musicians. Both tonal and non-tonal musicians also benefited more from increasing stimulus duration in processing pitch changes than non-musicians and they generally require less time for pitch processing. Musicians were also more sensitive to intrinsic F0 in pitch perception and differences of pitch types.ConclusionThe effect of musical training strengthens categorical perception more consistently in non-tonal speakers than tonal speakers. Overall, musicians benefit more from increased stimulus duration, due perhaps to their greater sensitivity to temporal information, thus allowing them to be better at forming a more robust auditory representation and matching sounds to internalized memory templates. Musicians also attended more to acoustic details such as intrinsic F0 and pitch types in pitch processing, and yet, overall, their categorization of pitch was not compromised by traces of these acoustic details from their auditory short-term working memory. These findings may lead to a better understanding of pitch perception deficits in special populations, particularly among individuals diagnosed with autism spectrum disorder (ASD).

The Effect of Recording Montage and Tone Burst Duration on Cervical and Ocular Vestibular Evoked Myogenic Potential Latency and Amplitude.

Objectives The objectives of this study were (a) to investigate the optimal tone burst duration when recording the cervical vestibular evoked myogenic potential (cVEMP) and the ocular vestibular evoked myogenic potential (oVEMP) and (b) to determine whether monopolar recording influences the latency or amplitude of the cVEMP or the oVEMP. Method Fifteen subjects ( M = 27.7 years, SD = 6.73 years) participated in this study. The participants had no prior history of otological or neurological disease. Both oVEMPs and cVEMPs were recorded at a fixed stimulus level for stimulus durations of 2, 5, 10, and 25 ms. For both cVEMP and oVEMP, responses were obtained using a traditional differential recording montage and a monopolar recording montage. Results The cVEMP and the oVEMP had the greatest amplitude in the 2-ms stimulus condition. There was a statistically significant decrease in amplitude for durations greater than 2 ms. Monopolar and bipolar cVEMP and oVEMP latencies and amplitudes were not significantly different. Conclusion As stimulus duration increased beyond 2 ms, the amplitude of the response decreased for both the cVEMP and the oVEMP. There was no significant change in latency with increasing stimulus duration for either response. These results suggested the optimal stimulus duration for both the oVEMP and cVEMP is 2 ms, and there is no apparent advantage of using a bipolar recording technique.

Optimum Number of Sweeps in Clinical OVEMP Recording; How Many Sweeps are Necessary?

Ocular vestibular-evoked myogenic potentials (OVEMPs) in our hands provide us with reproducible and consistent results; however, it has been shown that the OVEMP amplitude decreases with increased stimulus duration. The exact number of stimuli for OVEMP recording is not consistent among the published papers describing this test. We aimed to determine the number of stimuli needed to produce a satisfactory OVEMP response and the consequences of a more prolonged stimulation to the OVEMP response. We retrospectively analyzed 50 OVEMP patient recordings and found that the average number of sweeps carried out was 26. We carried out three different OVEMP recordings using our standard protocol of (1) a "standard" OVEMP protocol, in which we record until the OVEMP wave becomes obvious; (2) an OVEMP recording using our average of 26 sweeps; and (3) an OVEMP recording with twice as many sweeps. OVEMP latencies did not change when using different number of sweeps; however, the amplitudes showed a significant decrease with an increasing number of sweeps. OVEMPs can be completed in a satisfactory manner with a much lower number of stimuli than those usually carried out. Reducing the stimulus number reduces the time taken for the test, minimizes the cochlear insult while not reducing the valuable information obtained, and maximizes the amplitude of the stimulus, possibly increasing the accuracy of measuring interaural amplitudes and helping to measure asymmetry.

Audiovisual Interactions in Front and Rear Space.

The human visual and auditory systems do not encode an entirely overlapped space when static head and body position are maintained. While visual capture of sound source location in the frontal field is known to be immediate and direct, visual influence in the rear auditory space behind the subject remains under-studied. In this study we investigated the influence of presenting frontal LED flashes on the perceived location of a phantom sound source generated using time-delay-based stereophony. Our results show that frontal visual stimuli affected auditory localization in two different ways – (1) auditory responses were laterally shifted (left or right) toward the location of the light stimulus and (2) auditory responses were more often in the frontal field. The observed visual effects do not adhere to the spatial rule of multisensory interaction with regard to the physical proximity of cues. Instead, the influence of visual cues interacted closely with front–back confusions in auditory localization. In particular, visually induced shift along the left–right direction occurred most often when an auditory stimulus was localized in the same (frontal) field as the light stimulus, even when the actual sound sources were presented from behind a subject. Increasing stimulus duration (from 15-ms to 50-ms) significantly mitigated the rates of front–back confusion and the associated effects of visual stimuli. These findings suggest that concurrent visual stimulation elicits a strong frontal bias in auditory localization and confirm that temporal integration plays an important role in decreasing front–back errors under conditions requiring multisensory spatial processing.

In vitro single-unit recordings reveal increased peripheral nerve conduction velocity by focused pulsed ultrasound

Ultrasound that is widely used in medical diagnosis has drawn growing interests as a noninvasive means of neuromodulation. Focused pulsed ultrasound (FPUS) effectively modulates neural encoding and transmission in the peripheral nervous system (PNS) with unclear mechanism of action, which is further confounded by contradictory experimental outcomes from recordings of compound action potentials (CAP). To address that, we developed a novel in vitro set up to achieve simultaneous single-unit recordings from individual mouse sciatic nerve axon and systematically studied the neuromodulation effects of FPUS on individual axon. Unlike previous CAP recordings, our single-unit recordings afford superior spatial and temporal resolution to reveal the subtle but consistent effects of ultrasonic neuromodulation. Our results indicate that, (1) FPUS did not evoke action potentials directly in mouse sciatic nerve at all the tested intensities (spatial peak temporal average intensity, ISPTA of 0.91 to 28.2 W/cm2); (2) FPUS increases the nerve conduction velocity (CV) in both fast-conducting A- and slow-conducting C- type axons with effects more pronounced at increased stimulus duration and intensity; and (3) effects of increased CV is reversible and cannot be attributed to the change of local temperature. Our results support existing theories of non-thermal mechanisms underlying ultrasonic neuromodulation with low-intensity FPUS, including NICE, flexoelectricity, and solition models. This work also provides a solid experimental basis to further advance our mechanistic understandings of ultrasonic neuromodulation in the PNS.

Electric stimulus duration alters network-mediated responses depending on retinal ganglion cell type

Objective. To improve the quality of artificial vision that arises from retinal prostheses, it is important to bring electrically-elicited neural activity more in line with the physiological signaling patterns that arise normally in the healthy retina. Our previous study reported that indirect activation produces a closer match to physiological responses in ON retinal ganglion cells (RGCs) than in OFF cells (Im and Fried 2015 J. Physiol. 593 3677–96). This suggests that a preferential activation of ON RGCs would shape the overall retinal response closer to natural signaling. Recently, we found that changes to the rate at which stimulation was delivered could bias responses towards a stronger ON component (Im and Fried 2016a J. Neural Eng. 13 025002), raising the possibility that changes to other stimulus parameters can similarly bias towards stronger ON responses. Here, we explore the effects of changing stimulus duration on the responses in ON and OFF types of brisk transient (BT) and brisk sustained (BS) RGCs. Approach. We used cell-attached patch clamp to record RGC spiking in the isolated rabbit retina. Targeted RGCs were first classified as ON or OFF type by their light responses, and further sub-classified as BT or BS types by their responses to both light and electric stimuli. Spiking in targeted RGCs was recorded in response to electric pulses with durations varying from 5 to100 ms. Stimulus amplitude was adjusted at each duration to hold total charge constant for all experiments. Main results. We found that varying stimulus durations modulated responses differentially for ON versus OFF cells: in ON cells, spike counts decreased significantly with increasing stimulus duration while in OFF cells the changes were more modest. The maximum ratio of ON versus OFF responses occurred at a duration of ~10 ms. The difference in response strength for BT versus BS cells was much larger in ON cells than in OFF cells. Significance. The stimulation rates preferred by subjects during clinical trials are similar to the rates that maximize the ON/OFF response ratio in in vitro testing (Im and Fried 2016a J. Neural Eng. 13 025002). Here, we determine the stimulus duration that produces the strongest bias towards ON responses and speculate that it will further enhance clinical effectiveness.

Investigation of the BOLD and CBV fMRI responses to somatosensory stimulation in awake marmosets (Callithrix jacchus).

Understanding the spatiotemporal features of the hemodynamic response function (HRF) to brain stimulation is essential for the correct application of neuroimaging methods to study brain function. Here, we investigated the spatiotemporal evolution of the blood oxygen level-dependent (BOLD) and cerebral blood volume (CBV) HRF in conscious, awake marmosets (Callithrix jacchus), a New World non-human primate with a lissencephalic brain and with growing use in biomedical research. The marmosets were acclimatized to head fixation and placed in a 7-T magnetic resonance imaging (MRI) scanner. Somatosensory stimulation (333-μs pulses; amplitude, 2mA; 64Hz) was delivered bilaterally via pairs of contact electrodes. A block design paradigm was used in which the stimulus duration increased in pseudo-random order from a single pulse up to 256 electrical pulses (4s). For CBV measurements, 30mg/kg of ultrasmall superparamagnetic ironoxide particles (USPIO) injected intravenously, were used. Robust BOLD and CBV HRFs were obtained in the primary somatosensory cortex (S1), secondary somatosensory cortex (S2) and caudate at all stimulus conditions. In particular, BOLD and CBV responses to a single 333-μs-long stimulus were reliably measured, and the CBV HRF presented shorter onset time and time to peak than the BOLD HRF. Both the size of the regions of activation and the peak amplitude of the HRFs grew quickly with increasing stimulus duration, and saturated for stimulus durations greater than 1s. Onset times in S1 and S2 were faster than in caudate. Finally, the fine spatiotemporal features of the HRF in awake marmosets were similar to those obtained in humans, indicating that the continued refinement of awake non-human primate models is essential to maximize the applicability of animal functional MRI studies to the investigation of human brain function.

Comparison of photopic negative response (PhNR) between focal macular and full-field electroretinograms in monkeys.

To compare the characteristics of the photopic negative response (PhNR) between the focal macular and full-field electroretinograms (ERGs) in monkeys. Both focal macular and full-field photopic ERGs were recorded in four cynomolgus monkeys under identical stimulus and recording conditions except for which area of the retina was illuminated. The luminance and duration of red flash stimuli were varied in the presence of steady blue background illumination. These ERGs were recorded before and after intravitreal injection of tetrodotoxin (TTX). Several differences were identified between the focal macular and full-field ERGs, including: (1) The PhNR/b-wave amplitude ratio was higher in the focal macular than in the full-field ERGs, and (2) the stimulus threshold of the focal macular PhNR was lower than that of the full-field PhNR. For both macular and full-field stimulation conditions, (1) PhNR amplitude generally increased with increasing stimulus luminance; (2) PhNR implicit time was independent of the stimulus luminance; (3) PhNR amplitude and implicit time increased with increasing stimulus duration up to 50ms, while a further increase in stimulus duration produced no change in amplitude or implicit time; and (4) PhNR amplitude was selectively attenuated by TTX. Both the focal macular and full-field PhNRs reflect the functional properties of the inner retina including the retinal ganglion cells (RGCs). Relative to the b-wave, the contribution is weighted more heavily in the focal macular than in the full-field PhNR. Furthermore, these results support the idea that the focal macular PhNR can be an indicator of the function of the macular RGCs.

Classification of odorants across layers in locust olfactory pathway.

Olfactory processing takes place across multiple layers of neurons from the transduction of odorants in the periphery, to odor quality processing, learning, and decision making in higher olfactory structures. In insects, projection neurons (PNs) in the antennal lobe send odor information to the Kenyon cells (KCs) of the mushroom bodies and lateral horn neurons (LHNs). To examine the odor information content in different structures of the insect brain, antennal lobe, mushroom bodies and lateral horn, we designed a model of the olfactory network based on electrophysiological recordings made in vivo in the locust. We found that populations of all types (PNs, LHNs, and KCs) had lower odor classification error rates than individual cells of any given type. This improvement was quantitatively different from that observed using uniform populations of identical neurons compared with spatially structured population of neurons tuned to different odor features. This result, therefore, reflects an emergent network property. Odor classification improved with increasing stimulus duration: for similar odorants, KC and LHN ensembles reached optimal discrimination within the first 300-500 ms of the odor response. Performance improvement with time was much greater for a population of cells than for individual neurons. We conclude that, for PNs, LHNs, and KCs, ensemble responses are always much more informative than single-cell responses, despite the accumulation of noise along with odor information.

Vibrotactile timing: Are vibrotactile judgements of duration affected by repetitive stimulation?

Timing in the vibrotactile modality was explored. Previous research has shown that repetitive auditory stimulation (in the form of click-trains) and visual stimulation (in the form of flickers) can alter duration judgements in a manner consistent with a "speeding up" of an internal clock. In Experiments 1 and 2 we investigated whether repetitive vibrotactile stimulation in the form of vibration trains would also alter duration judgements of either vibrotactile stimuli or visual stimuli. Participants gave verbal estimates of the duration of vibrotactile and visual stimuli that were preceded either by five seconds of 5-Hz vibration trains, or, by a five-second period of no vibrotactile stimulation, the end of which was signalled by a single vibration pulse (control condition). The results showed that durations were overestimated in the vibrotactile train conditions relative to the control condition; however, the effects were not multiplicative (did not increase with increasing stimulus duration) and as such were not consistent with a speeding up of the internal clock, but rather with an additive attentional effect. An additional finding was that the slope of the vibrotactile psychometric (control condition) function was not significantly different from that of the visual (control condition) function, which replicates a finding from a previous cross-modal comparison of timing.

Increasing stimulus duration improves attention and memory performance in elderly with cognitive impairment.

Objectives:In this study, we investigated whether increasing stimulus duration could improve performance on a test of attention and short-term memory in cognitively impaired individuals.Methods:A computer-generated forward digit span test was administered to 65 patients with mild cognitive impairment or dementia (28 intervention and 37 controls). After point of failure, testing in the intervention group was continued at the same rate, but with an average 150% digit lengthening to 800 ms. Testing of controls was continued using the standard digit span test.Results:In the intervention group, 13/28 (46.4%) improved their digit span test performance, compared to 2/37 (5.4%) in the control group (p = 0.00005).Conclusion:Cognitively impaired elderly participants improved performance on a test of attention and short-term memory, when stimulus duration was increased in proportion to elongation of the finger tap touch-phase previously found in a similar cohort. A possible mechanism for the effect of increased stimulus duration on attention and short-term memory is discussed.

Increasing stimulus duration can normalize late-positive event related potentials in people with schizophrenia: Possible implications for understanding cognitive deficits

This study determined whether increasing stimulus duration for patients with schizophrenia normalized late Event Related Potentials (ERPs) associated with modulation of response to emotion-evoking stimuli. These ERPs are decreased in patients versus healthy controls when both view stimuli of the same duration. Subjects viewed pictures of hands and judged whether the events depicted were painful or non-painful. Pictures were presented to patients for 500 or 800ms and to healthy controls for 200 or 500ms. Participants were 19 adult outpatients meeting DSM-IV criteria for schizophrenia or schizoaffective disorder and 18 healthy controls, as assessed by the Structured Clinical Interview. ERPs to neutral stimuli during a 350–900ms window following stimulus onset were subtracted from ERPs during this same response window to pain stimuli. The area under this difference wave reflected the degree of pain-related positivity and was the dependent measure for analysis. Patient late-positive ERP responses following 500 and 800ms stimuli were highly similar to responses in healthy controls following 200 and 500ms stimuli respectively. Patients and controls differed significantly when responses to 500ms stimuli were compared. People with schizophrenia are known to process information more slowly than healthy people. Our results indicate that slowed early processing of sensory input may limit engagement of higher cognitive and regulatory processes in patients with schizophrenia. This may be one reason that self-regulation is compromised in patients, and may help explain why measures of slowed information processing account for so much variance in other cognitive deficits in schizophrenia.