Sequential dependencies in pitch judgments

Opposing serial effects of stimulus and choice in speech perception scale with context variability

In this study, we investigated serial effects on the perception of auditory vowel stimuli across three experimental setups with different degrees of context variability. Aligning with recent findings in visual perception, our results confirm the existence of two distinct processes in serial dependence: a repulsive sensory effect coupled with an attractive decisional effect. Importantly, our study extends these observations to the auditory domain, demonstrating parallel serial effects in audition. Furthermore, we uncover context variability effects, revealing a linear pattern for the repulsive perceptual effect and a quadratic pattern for the attractive decisional effect. These findings support the presence of adaptive sensory mechanisms underlying the repulsive effects, while higher-level mechanisms appear to govern the attractive decisional effect. The study provides valuable insights into the interplay of attractive and repulsive serial effects in auditory perception and contributes to our understanding of the underlying mechanisms.

A novel method for estimating properties of attentional oscillators reveals an age-related decline in flexibility

Dynamic attending theory proposes that the ability to track temporal cues in the auditory environment is governed by entrainment, the synchronization between internal oscillations and regularities in external auditory signals. Here, we focused on two key properties of internal oscillators: their preferred rate, the default rate in the absence of any input; and their flexibility, how they adapt to changes in rhythmic context. We developed methods to estimate oscillator properties (Experiment 1) and compared the estimates across tasks and individuals (Experiment 2). Preferred rates, estimated as the stimulus rates with peak performance, showed a harmonic relationship across measurements and were correlated with individuals' spontaneous motor tempo. Estimates from motor tasks were slower than those from the perceptual task, and the degree of slowing was consistent for each individual. Task performance decreased with trial-to-trial changes in stimulus rate, and responses on individual trials were biased toward the preceding trial's stimulus properties. Flexibility, quantified as an individual's ability to adapt to faster-than-previous rates, decreased with age. These findings show domain-specific rate preferences for the assumed oscillatory system underlying rhythm perception and production, and that this system loses its ability to flexibly adapt to changes in the external rhythmic context during aging.

Opposing serial dependencies revealed for sequences of auditory emotional stimuli

Our percept of the world is not solely determined by what we perceive and process at a given moment in time, but also depends on what we processed recently. In the present study, we investigate whether the perceived emotion of a spoken sentence is contingent upon the emotion of an auditory stimulus on the preceding trial (i.e., serial dependence). Thereto, participants were exposed to spoken sentences that varied in emotional affect by changing the prosody that ranged from 'happy' to 'fearful'. Participants were instructed to rate the emotion. We found a positive serial dependence for emotion processing whereby the perceived emotion was biased towards the emotion on the preceding trial. When we introduced 'no-go' trials (i.e., no rating was required), we found a negative serial dependence when participants knew in advance to withhold their response on a given trial (Experiment 2) and a positive serial dependence when participants received the information to withhold their response after the stimulus presentation (Experiment 3). We therefore established a robust serial dependence for emotion processing in speech and introduce a methodology to disentangle perceptual from post-perceptual processes. This approach can be applied to the vast majority of studies investigating sequential dependencies to separate positive from negative serial dependence.

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.

Reliable estimation of internal oscillator properties from a novel, fast-paced tapping paradigm

Rhythmic structure in speech, music, and other auditory signals helps us track, anticipate, and understand the sounds in our environment. The dynamic attending framework proposes that biological systems possess internal rhythms, generated via oscillatory mechanisms, that synchronize with (entrain to) rhythms in the external world. Here, we focused on two properties of internal oscillators: preferred rate, the default rate of an oscillator in the absence of any input, and flexibility, the oscillator's ability to adapt to changes in external rhythmic context. We aimed to develop methods that can reliably estimate preferred rate and flexibility on an individual basis. The experiment was a synchronization-continuation finger tapping paradigm with a unique design: the stimulus rates were finely sampled over a wide range of rates and were presented only once. Individuals tapped their finger to 5-event isochronous stimulus sequences and continued the rhythm at the same pace. Preferred rate was estimated by assessing the best-performance conditions where the difference between the stimulus rate and continuation tapping rate (tempo-matching error) was minimum. The results revealed harmonically related, multiple preferred rates for each individual. We maximized the differences in stimulus rate between consecutive trials to challenge individuals' flexibility, which was then estimated by how much tempo-matching errors in synchronization tapping increase with this manipulation. Both measures showed test-retest reliability. The findings demonstrate the influence of properties of the auditory context on rhythmic entrainment, and have implications for development of methods that can improve attentional synchronization and hearing.

Propagation and update of auditory perceptual priors through alpha and theta rhythms

To maintain a continuous and coherent percept over time, the brain makes use of past sensory information to anticipate forthcoming stimuli. We recently showed that auditory experience of the immediate past is propagated through ear-specific reverberations, manifested as rhythmic fluctuations of decision bias at alpha frequencies. Here, we apply the same time-resolved behavioural method to investigate how perceptual performance changes over time under conditions of stimulus expectation and to examine the effect of unexpected events on behaviour. As in our previous study, participants were required to discriminate the ear-of-origin of a brief monaural pure tone embedded in uncorrelated dichotic white noise. We manipulated stimulus expectation by increasing the target probability in one ear to 80%. Consistent with our earlier findings, performance did not remain constant across trials, but varied rhythmically with delay from noise onset. Specifically, decision bias showed a similar oscillation at ~9 Hz, which depended on ear congruency between successive targets. This suggests rhythmic communication of auditory perceptual history occurs early and is not readily influenced by top-down expectations. In addition, we report a novel observation specific to infrequent, unexpected stimuli that gave rise to oscillations in accuracy at ~7.6 Hz one trial after the target occurred in the non-anticipated ear. This new behavioural oscillation may reflect a mechanism for updating the sensory representation once a prediction error has been detected.

Gradual decay and sudden death of short-term memory for pitch

The ability to discriminate frequency differences between pure tones declines as the duration of the interstimulus interval (ISI) increases. The conventional explanation for this finding is that pitch representations gradually decay from auditory short-term memory. Gradual decay means that internal noise increases with increasing ISI duration. Another possibility is that pitch representations experience "sudden death," disappearing without a trace from memory. Sudden death means that listeners guess (respond at random) more often when the ISIs are longer. Since internal noise and guessing probabilities influence the shape of psychometric functions in different ways, they can be estimated simultaneously. Eleven amateur musicians performed a two-interval, two-alternative forced-choice frequency-discrimination task. The frequencies of the first tones were roved, and frequency differences and ISI durations were manipulated across trials. Data were analyzed using Bayesian models that simultaneously estimated internal noise and guessing probabilities. On average across listeners, internal noise increased monotonically as a function of increasing ISI duration, suggesting that gradual decay occurred. The guessing rate decreased with an increasing ISI duration between 0.5 and 2 s but then increased with further increases in ISI duration, suggesting that sudden death occurred but perhaps only at longer ISIs. Results are problematic for decay-only models of discrimination and contrast with those from a study on visual short-term memory, which found that over similar durations, visual representations experienced little gradual decay yet substantial sudden death.

Neural and Behavioral Evidence for Frequency-Selective Context Effects in Rhythm Processing in Humans

When listening to music, people often perceive and move along with a periodic meter. However, the dynamics of mapping between meter perception and the acoustic cues to meter periodicities in the sensory input remain largely unknown. To capture these dynamics, we recorded the electroencephalography while nonmusician and musician participants listened to nonrepeating rhythmic sequences, where acoustic cues to meter frequencies either gradually decreased (from regular to degraded) or increased (from degraded to regular). The results revealed greater neural activity selectively elicited at meter frequencies when the sequence gradually changed from regular to degraded compared with the opposite. Importantly, this effect was unlikely to arise from overall gain, or low-level auditory processing, as revealed by physiological modeling. Moreover, the context effect was more pronounced in nonmusicians, who also demonstrated facilitated sensory-motor synchronization with the meter for sequences that started as regular. In contrast, musicians showed weaker effects of recent context in their neural responses and robust ability to move along with the meter irrespective of stimulus degradation. Together, our results demonstrate that brain activity elicited by rhythm does not only reflect passive tracking of stimulus features, but represents continuous integration of sensory input with recent context.

Local context effects in the magnitude-duration illusion: Size but not numerical value sequentially alters perceived duration

Many aspects of an event can change perceived duration. A common example of this is the magnitude-duration illusion, in which a high magnitude (e.g. large or high value) stimulus will be perceived to last longer than a low magnitude stimulus. The effects of magnitude on perceived duration are normally considered in terms of global context effects; what is large depends on the stimuli used throughout the experiment. In the current article, we examine local context effects in the magnitude-duration illusion, how trial-by-trial changes in magnitude affect the subjective duration of an event. We performed two experiments in which numerical magnitude and stimulus size were varied within either the example phase or reproduction phase of a temporal reproduction task. We showed that in the current trial the combined value-size magnitude presented in the example phase affected subsequent reproductions, while the magnitude presented in the reproduction phase did not. The size magnitude presented in the reproduction phase also affected the reproduction in the following trial, such that a larger stimulus in the current reproduction phase resulted in shorter reproductions in the next reproduction phase. This indicates that low level stimulus properties (i.e. size) can act to contextualize subsequent stimulus properties, which in turn affect perceived duration. The findings of our experiments add local, low-level, context effects to the known modifiers of perceived duration, as well as provide evidence with regards to the role of magnitude in interval timing.

Auditory Perceptual History Is Propagated through Alpha Oscillations

Perception is a proactive, “predictive” process, in which the brain relies, at least in part, on accumulated experience to make best guesses about the world to test against sensory data, updating the guesses as new experience is acquired. Using novel behavioral methods, the present study demonstrates the role of alpha rhythms in communicating past perceptual experience. Participants were required to discriminate the ear of origin of brief sinusoidal tones that were presented monaurally at random times within a burst of uncorrelated dichotic white noise masks. Performance was not constant but varied with delay after noise onset in an oscillatory manner at about 9 Hz (alpha rhythm). Importantly, oscillations occurred only for trials preceded by a target tone to the same ear, either on the previous trial or two trials back. These results suggest that communication of perceptual history generates neural oscillations within specific perceptual circuits, strongly implicating behavioral oscillations in predictive perception and with formation of working memory.

•

We demonstrate the role of alpha rhythms in the propagation of perceptual history

•

Auditory decisions were rhythmically biased by stimuli presented 1 or 2 trials back

•

Bias oscillated at ∼9 Hz only when successive stimuli occurred in the same ear

•

Alpha is strongly implicated in predictive perception and working memory formation

Visual serial dependence in an audiovisual stimulus

Serial dependence is a phenomenon that biases the perception of features or objects systematically toward sensory input from the recent past (Fischer & Whitney, 2014). There is an active debate whether this effect is rooted directly in perception or reflects biases in decision making. We investigated serial dependence across three experiments by manipulating the decision made on each trial. A multimodal audiovisual stimulus comprising a Gabor and a vowel sound was presented repeatedly. On each trial, participants reported either the Gabor orientation or the vowel sound. Participants either ignored one modality (Experiment 1) or attended to both modalities (Experiments 2 and 3). In Experiments 2 and 3, the response task was randomized to prevent anticipating which modality to respond to until the response phase. In Experiment 3, no-response trials were additionally interleaved. Results across the three experiments demonstrated serial dependence only when participants reported the visual modality. Serial dependence was also present in visual reports when participants completed auditory reports or made no reports on previous trials. The previous stimulus alone was enough to elicit an effect. Serial dependence is unlikely to be an effect of the previous decision on the stimulus, but rather an effect of perceiving the previous stimulus.

Decay of internal reference information in duration discrimination: Intertrial interval modulates the Type B effect

Psychophysical evidence suggests that human perception of a stimulus is assimilated towards previous stimuli. The internal reference model (IRM) explains such assimilation through an internal reference (IR), which integrates past and present stimulus representations and thus might be conceived as a form of perceptual memory. In this study, we investigated whether the IR decays with time, as previously shown for perceptual memory representations in general. One specific prediction of IRM is higher discrimination sensitivity when a constant standard precedes rather than follows a variable comparison in a two-alternative forced-choice (2AFC) discrimination task. Furthermore, the magnitude of this so-called negative Type B effect should decrease with decreasing weighting of past stimulus information in the integration process. Therefore, decay of the IR should result in a reduced Type B effect. To examine this prediction, we carried out a 2AFC duration discrimination experiment with a short (1,600 ms) and a long (3,200 ms) intertrial interval (ITI). As expected, a reduced negative Type B effect was observed at the long compared with the short ITI, consistent with the idea that humans rely on the immediate past when evaluating current sensory input, however, less so when the IR incorporating the perceptual short-term memory representation of these past stimuli has already decayed.