Direction Of Rate Change Research Articles

Electrophysiological and Psychophysical Measures of Temporal Pitch Sensitivity in Normal-hearing Listeners

To obtain combined behavioural and electrophysiological measures of pitch perception, we presented harmonic complexes, bandpass filtered to contain only high-numbered harmonics, to normal-hearing listeners. These stimuli resemble bandlimited pulse trains and convey pitch using a purely temporal code. A core set of conditions consisted of six stimuli with baseline pulse rates of 94, 188 and 280 pps, filtered into a HIGH (3365–4755 Hz) or VHIGH (7800–10,800 Hz) region, alternating with a 36% higher pulse rate. Brainstem and cortical processing were measured using the frequency following response (FFR) and auditory change complex (ACC), respectively. Behavioural rate change difference limens (DLs) were measured by requiring participants to discriminate between a stimulus that changed rate twice (up-down or down-up) during its 750-ms presentation from a constant-rate pulse train. FFRs revealed robust brainstem phase locking whose amplitude decreased with increasing rate. Moderate-sized but reliable ACCs were obtained in response to changes in purely temporal pitch and, like the psychophysical DLs, did not depend consistently on the direction of rate change or on the pulse rate for baseline rates between 94 and 280 pps. ACCs were larger and DLs lower for stimuli in the HIGH than in the VHGH region. We argue that the ACC may be a useful surrogate for behavioural measures of rate discrimination, both for normal-hearing listeners and for cochlear-implant users. We also showed that rate DLs increased markedly when the baseline rate was reduced to 48 pps, and compared the behavioural and electrophysiological findings to recent cat data obtained with similar stimuli and methods.

Asymmetry of strain rate sensitivity between up- and down-changes in 6000 series aluminium alloys of varying Si content

Increasing demand for a reduction in fuel emissions in passenger vehicles has generated the need for lighter weight materials to be used in automobile manufacture for body-in-white applications. Aluminium alloys in the 6000-series, containing Mg and Si are ideal candidates for these applications but lack the formability found in commonly used steels, providing a need to more fully understand the factors influencing the formability of these alloys at high strains. Conventionally, a high strain rate sensitivity (SRS) is tied to increased formability because it retards the increase in the local strain rate found in the diffuse neck interior. However, most experimental work neglects that the regions exterior to the neck will undergo a local decrease in the strain rate which causes a corresponding material softening. Observations of an asymmetry between up-change and down-change SRS of these alloys in the natural aged condition show that different mechanisms are controlling the SRS depending on the direction of rate change. Following a characterization of the state of clustering by differential scanning calorimetry, continuous tensile and precision strain rate sensitivity testing results are presented, elucidating the differences between the up-change and down-change SRS tests. It is shown that these differences are due to the activation of different thermal obstacles during the two directions of rate changes. The role of a change in Si content on the mechanical properties is explored and its suspected role on the asymmetric SRS is discussed.

Intraday volatility responses to monetary policy events

This paper explores the effects of US monetary policy events on intraday volatility in the US equity markets. We examine Federal Open Market Committee (FOMC) announcements as well as real-time changes in market expectations about future policy announcements and their impact on the intraday volatility dynamics of the S&P 500 index. The analysis shows elevated intraday volatility following FOMC announcements through the market close, with a spike at the time of the announcement. We then differentiate the volatility spike by modeling an asymmetric response based on the direction of the actual target rate change. Our results suggest that the size of the volatility spike is dependent on the direction of the rate change, with expansionary monetary policy actions having a larger spike than contractionary policy actions. The duration of these volatility spikes is relatively short-lived, with the spike dampening out within 15 minutes. A more lasting impact is, however, documented for real-time changes in market expectations where the volatility spike tends to persist for at least one hour.

Delayed adaptation of ventricular repolarization after sudden changes in heart rate due to conversion of atrial fibrillation. A potential risk factor for proarrhythmia?

Onset and termination of atrial fibrillation are often associated with abrupt changes in heart rate. Presence and time-course of delayed adaptation of the QT/QTc interval are unknown, but a temporary "mismatch" between rate and the QT interval may enhance the risk of proarrhythmia. In a prospective two-part study, time-course of adaptation of ventricular repolarization after abrupt changes in heart rate was assessed during termination of Holter ECG-documented atrial fibrillation episodes (Group 1, 32 patients) and subsequently in 20 patients with sick sinus syndrome and cardiac pacing initiating abrupt bi-directional changes in paced heart rate (Group 2). Conversion of atrial fibrillation showed a 32+/-21 bpm fall in heart rate (P<0.05). Restoration of the QTc interval afterwards was delayed by < or =1 min in 27%, by 1-2 min in 21%, by 2-5 min in 11% and by >5 min in 41% of the cases. Atrial pacing simulating a 30 bpm fall/increase in atrial rate demonstrated that a subsequent transient rate-QT mismatch is a physiological phenomenon (fall of 100 to 70 bpm: initially 90% of the proper QTc interval, compared with 94% after conversion of atrial fibrillation). The restoration curve of QTc adaptation showed an initially fast and subsequently slower time component, with interindividual variation. Clinical parameters, baseline heart rate or the direction of rate changes were not predictive. Delayed adaptation of ventricular repolarization following atrial fibrillation onset and termination is common, requiring minutes for restoring the QT/QTc steady state. Clinical parameters fail to predict patients with a long-lasting rate-QT mismatch. It may carry a significant arrhythmogenic risk particularly in patients on QT altering medication.

Proportion of Correct Detections of Rate Changes in Pulsed Stimuli

Two groups of 12 listeners each were required to detect and report—within a 5-sec interval—changes in the rate of ongoing square-wave pulses of 2 and 11 pulses/sec. One group was given preknowledge of the direction of rate change; the other was not. Blank trials, where no change in rate occurred, were inserted randomly into the trial sequences. High proportions of correct detections were associated with short reaction times and conversely. Preknowledge of the direction of rate change produced no significant effects. The proportion of correct detections was higher for accelerations than for decelerations only at a basal repetition rate of 11 pulses/sec. The percent-correct detection measure closely paralleled the reaction time measure previously employed by us. Performance efficiency was not affected by the 5-sec time limitation imposed.