Perceptual Onset Research Articles

Cognitive control and right ventrolateral prefrontal cortex: reflexive reorienting, motor inhibition, and action updating

Delineating the functional organization of the prefrontal cortex is central to advancing models of goal-directed cognition. Considerable evidence indicates that specific forms of cognitive control are associated with distinct subregions of the left ventrolateral prefrontal cortex (VLPFC), but less is known about functional specialization within the right VLPFC. We report a functional MRI meta-analysis of two prominent theories of right VLPFC function: stopping of motor responses and reflexive orienting to abrupt perceptual onsets. Along with a broader review of right VLPFC function, extant data indicate that stopping and reflexive orienting similarly recruit the inferior frontal junction (IFJ), suggesting that IFJ supports the detection of behaviorally relevant stimuli. By contrast, other right VLPFC subregions are consistently active during motor inhibition, but not reflexive reorienting tasks, with posterior-VLPFC being active during the updating of action plans and mid-VLPFC responding to decision uncertainty. These results highlight the rich functional heterogeneity that exists within right VLPFC.

Chinese characters reveal impacts of prior experience on very early stages of perception

BackgroundVisual perception is strongly determined by accumulated experience with the world, which has been shown for shape, color, and position perception, in the field of visuomotor learning, and in neural computation. In addition, visual perception is tuned to statistics of natural scenes. Such prior experience is modulated by neuronal top-down control the temporal properties of which had been subject to recent studies. Here, we deal with these temporal properties and address the question how early in time accumulated past experience can modulate visual perception.ResultsWe performed stimulus discrimination experiments and compared a group of Chinese participants with a German control group. The perception of our briefly presented visual objects (targets) was disturbed by masking stimuli which appeared in close spatiotemporal proximity. These masking stimuli were either intact or scrambled Chinese characters and did not overlap with the targets. In contrast to German controls, Chinese participants show substantial performance differences for real versus scrambled Chinese characters if these masking stimuli were presented as early as less than 100 milliseconds after the onset of the target. For Chinese observers, it even occured that meaningful masking stimuli enhanced target identification if they were shown at least 100 milliseconds after target onset while the same stimuli impaired recognition if presented in close temporal proximity to the target. The latter finding challenges interpretations of our data that solely rely on stimulus contours or geometric properties and emphasizes the impact of prior experience on the very early temporal dynamics of the visual system.ConclusionsOur findings demonstrate that prior experience which had been accummulated long before the experiments can modulate the time course of perception intriguingly early, namely already immediately after the perceptual onset of a visual event. This modulation cannot solely operate as a feedback in response to the visual event but is rather a permanent effect.

Model cortical responses for the detection of perceptual onsets and beat tracking in singing

We describe a biophysically motivated model of auditory salience based on a model of cortical responses and present results that show that the derived measure of salience can be used to identify the position of perceptual onsets in a musical stimulus successfully. The salience measure is also shown to be useful to track beats and predict rhythmic structure in the stimulus on the basis of its periodicity patterns. We evaluate the method using a corpus of unaccompanied freely sung stimuli and show that the method performs well, in some cases better than state-of-the-art algorithms. These results deserve attention because they are derived from a general model of auditory processing and not an arbitrary model achieving best performance in onset detection or beat-tracking tasks.

Illusory Vowels Resulting from Perceptual Continuity: A Functional Magnetic Resonance Imaging Study

We used functional magnetic resonance imaging to study the neural processing of vowels whose perception depends on the continuity illusion. Participants heard sequences of two-formant vowels under a number of listening conditions. In the "vowel conditions," both formants were always present simultaneously and the stimuli were perceived as speech-like. Contrasted with a range of nonspeech sounds, these vowels elicited activity in the posterior middle temporal gyrus (MTG) and superior temporal sulcus (STS). When the two formants alternated in time, the "speech-likeness" of the sounds was reduced. It could be partially restored by filling the silent gaps in each formant with bands of noise (the "Illusion" condition) because the noise induced an illusion of continuity in each formant region, causing the two formants to be perceived as simultaneous. However, this manipulation was only effective at low formant-to-noise ratios (FNRs). When the FNR was increased, the illusion broke down (the "illusion-break" condition). Activation in vowel-sensitive regions of the MTG was greater in the illusion than in the illusion-break condition, consistent with the perception of Illusion stimuli as vowels. Activity in Heschl's gyri (HG), the approximate location of the primary auditory cortex, showed the opposite pattern, and may depend instead on the number of perceptual onsets in a sound. Our results demonstrate that speech-sensitive regions of the MTG are sensitive not to the physical characteristics of the stimulus but to the perception of the stimulus as speech, and also provide an anatomically distinct, objective physiological correlate of the continuity illusion in human listeners.

Biases in the perceived timing of perisaccadic perceptual and motor events

Subjects typically experience the temporal interval immediately following a saccade as longer than a comparable control interval. One explanation of this effect is that the brain antedates the perceptual onset of a saccade target to around the time of saccade initiation. This could explain the apparent continuity of visual perception across eye movements. This antedating account was tested in three experiments in which subjects made saccades of differing extents and then judged either the duration or the temporal order of key events. Postsaccadic stimuli underwent subjective temporal lengthening and had early perceived onsets. A temporally advanced awareness of saccade completion was also found, independently of antedating effects. These results provide convergent evidence supporting antedating and differentiating it from other temporal biases.

Illusory recouplings of onsets and terminations of glide tone components.

We present a new auditory illusion, the gap transfer illusion, supported by phenomenological and psychophysical data. In a typical situation, an ascending frequency glide of 2,500 msec with a temporal gap of 100 msec in the middle and a continuously descending frequency glide of 500 msec cross each other at their central positions. These glides move at the same constant speed in logarithmic frequency in opposite directions. The temporal gap in the long glide is perceived as if it were in the short glide. The same kind of subjective transfer of a temporal gap can take place also when the stimulus pattern is reversed in time. This phenomenon suggests that onsets and terminations of glide components behave as if they were independent perceptual elements. We also find that when two long frequency glides are presented successively with a short temporal overlap, a long glide tone covering the whole duration of the pattern and a short tone around the temporal middle can be perceived. To account for these results, we propose an event construction model, in which perceptual onsets and terminations are coupled to construct auditory events and the proximity principle connects these elements.

The role of eye movements and masking in monocular rivalry

Using an image stabilization technique, we have examined the role of eye movements on the phenomenon of monocular rivalry. Cross-correlation analysis confirms that perceptual onset of the vertical grating coincides with perceptual disappearance of the horizontal (and vice versa). Vertical and horizontal retinal image motion can modulate, selectively, the visibility of the horizontal and vertical gratings. However, a stable percept was observed when constant retinal image motion was matched for both vertical and horizontal components. These results support an eye-movement and afterimage explanation for the phenomenon of monocular rivalry (Georgeson, 1984). However, in addition to enhancing the visibility of a horizontal grating, a vertical “saccadic-like” retinal image motion decreased the visibility of the vertical component. This result is consistent with rivalry. That is, the visibility of both gratings are not independent, but are inversely related to each other. Our results are inconsistent with a hypothesis for monocular rivalry based upon inherently unstable neural interactions, but they also show that unstable fixational eye movements and afterimages are not the only factors determining the perceptual fluctuations.

The effect of a contralateral drone on the perceptual onset asynchrony of interaural tone sequences.

Several studies reported that subjects have difficulty in processing a sequence of auditory signals if the sequence alternates between ears: Alternating speech and melodies are recognized poorly. If, however, the ears not receiving this information are filled with noise or with a lower constant-frequency tone (drone), recognition improves again. This improvement is due to the fact that the signal is subjectively alternating to a much lesser extent. The present study was an attempt to measure the subjective ambient bandwidth within which the interaural signal moves when a contralateral drone is supplied. It turned out that the signal, although alternating between ears, appeared to arise from the middle of the head. The results were discussed in terms of auditory illusions.

The subjective tempo difference between interaural and monaural sequences as a function of sequence length.

Previous research has demonstrated that the subjective tempo of sequences of clicks that alternate between ears is slower than that of nonalternating sequences. Although the stimulus onset asynchronies (SOAs) between the clicks are the same in both conditions, their perceptual onset asynchronies (POAs) differ by 25 msec at all SOA values between 40 and 2,130 msec. It has been suggested that this subjective tempo difference originates only after a few clicks have been processed. The present study shows this not to be the case: The POA difference between interaural and monaural click sequences could also be established with sequences comprising only a few clicks.

The perceived tempi of coherent and streaming tone sequences: II.

Previous research demonstrated, by means of a reaction time technique, that there is no difference between the perceptual onset asynchronies (POAs) of nonalternating tone sequences and of frequency-alternating tone sequences, even if the latter are streaming. This finding implies that listeners are capable of extracting the tempo of the total alternating sequence, even though successive tones belong to different streams. The present study investigated whether subjects are also capable of establishing the tempo of one stream. To this end, listeners were required to match the rate of one stream by adjusting the rate of a nonalternating comparison stream (a pulse sequence). In addition, they were required to match the total rate of the streaming sequence. It turned out that the total tempo could be matched precisely and that the tempo of one stream could be approximated very closely.

The perceived tempi of coherent and streaming tone sequences.

Previous research has demonstrated that a sequence of tones that is alternated between ears is stretched out in echoic memory, as compared with monaural sequences. Although the stimulus onset asynchronies (SOAs) were the same in the interaural and monaural conditions, the perceptual onset asynchronies (POAs) differed by 24 msec. The present study investigated whether an analogous perceptual phenomenon exists for frequency-alternating tone sequences. It turned out that the POAs of coherent and even of streaming tone sequences were precisely the same as with nonalternating tone sequences.

The perceptual onset of musical tones.

The perceptual onset of a musical tone can be defined as the moment in time at which the stimulus is first perceived. In the present experiments, a simple threshold model for the perceptual onset was applied. A paradigm was used in which a sequence of tones had to be adjusted in such a way that the onsets were perceived at equally spaced moments in time. In Experiment 1, the threshold model was applied in a design in which the rise times of the tones were varied. We concluded that the perceptual onsets of the tones can, indeed, be defined as the times at which the envelopes pass a relative threshold of 15 dB below the maximum level of the tones (82 dB). In Experiment 2, the maximum levels of the tones were varied from 37 to 77 dB. The results show that there is a shift in the relative threshold, but that this shift is small relative to the shift in the stimulus level. In Experiment 3, the effect of level above masked threshold on the perceptual onset was investigated in more detail by varying the level of a background noise. The results show that the relative threshold decreases with increasing level above masked threshold. The results from our experiments strongly suggest that the relative threshold is linearly dependent on the level above masked or absolute threshold and that a 7-dB increment of this level results in a 1-dB relative threshold decrement. The threshold model is compared with a current temporal integration model for the perceptual onset of tones. It is shown that our data cannot be adequately explained by temporal integration. Our experimental results suggest that adaptation of the hearing mechanism to a certain relative stimulus level is responsible for perceptual onset. The applicability of our threshold model in various realistic musical situations is discussed.

Production and perception of segmental durations in spoken Japanese

As a step toward understanding the mechanisms by which segmental timing is determined, segmental durations are investigated both from the viewpoint of speech production and from that of speech perception using two-mora words consisting only of vowels. Assuming that the trajectories of formant frequencies can be approximated by step response functions of a critically damped second order system, the onset of articulatory control for the second vowel is estimated from the trajectories of formant frequencies, and is used as an index for the timing of the production of the second vowel. An analysis of the formant trajectories indicates considerable variability in the timing of production; the onset of the second vowel being earlier when articulatory differences between the first and second vowels are greater. On the other hand, the perceptual onset of the second vowel is determined by an identification test using truncated speech stimuli, and is used as an index for the timing of its perception. Results of the identification tests reveal comparatively small differences in perceptual timing, suggesting that the apparent diversity of timing at the level of speech production is induced to maintain the perceptual uniformity of segmental durations. [Work supported by Ministry of Education Grant-in-Aid for Scientific Research No. 31707.]

Effect of onset asymmetry upon the perceived onset of a CV during dichotic presentation

Data were gathered from four well-practiced subjects in a 2AFC paradigm which was subject driven, and allowed as many repeats of the stimulus pair as the subject requested prior to making his response. The stimuli consisted of the six stop-consonants followed by the vowel /a/. These natural speech CV's have served as stimuli in numerous dichotic speech perception studies. The results indicated that when the stimuli were separated by no more than 15 msec, the subjects could be divided into two homogeneous groups. One group was able to reliably determine a parallel pair of perceptual onset functions (one for each ear) which were of moderate slope and were separated by approximately 13 msec. The other group of subjects showed a reversal of the ear asymmetry and their perceptual onset functions had a zero slope. The results will be discussed in terms of its relevance to the temporal variables involved in dichotic CV experiments. [Supported by National Institutes of Health, USPHS Grant No. NS 11647-03.]

Effect of stimulus duration on perceptual onset and offset latencies

The effects of stimulus duration on perceptual onset and offset latency were compared in vision and audition. It was found that perceptual onset latency was independent of stimulus duration but that the perceptual offset latency was longer for brief stimuli than for stimuli that exceeded a critical duration. For stimuli longer than the critical duration, the perceptual onset and offset latencies were equal: The same temporal relationships were found in both modalities. The results indicate that for any specific stimulus parameters, reduction of stimulus duration results, ultimately, in a perception of fixed duration.