Using your required reading, review the article “Perceptual Asymmetry Induced by the Auditory Continuity Illusion.” Your article review should include the following:
·Introduction of the topic,
·author’s main point,
·description of what aspects of the neuroscience behind sensory and perceptual
·mechanisms come into play in this article,
·explanation of some of the key components of auditory stimulus in relation to the article,
·and personal analysis.
OBSERVATION Perceptual Asymmetry Induced by the Auditory Continuity Illusion Dorea R. Ruggles and Andrew J. Oxenham University of Minnesota The challenges of daily communication require listeners to integrate both independent and complementary auditory information to form holistic auditory scenes. As part of this process listeners are thought to fill in missing information to create continuous perceptual streams, even when parts of messages are masked or obscured. One example of this filling-in process—the auditory continuity illusion—has been studied primarily using stimuli presented in isolation, leaving it unclear whether the illusion occurs in more complex situations with higher perceptual and attentional demands. In this study, young normal-hearing participants listened for long target tones, either real or illusory, in “clouds” of shorter masking tone and noise bursts with pseudo- random spectrotemporal locations. Patterns of detection suggest that illusory targets are salient within mixtures, although they do not produce the same level of performance as the real targets. The results suggest that the continuity illusion occurs in the presence of competing sounds and can be used to aid in the detection of partially obscured objects within complex auditory scenes. Keywords: continuity illusion, auditory object, perceptual search, perceptual asymmetry The continuity illusion occurs when a masked or obscured portion of a stimulus is perceptually “filled in” to create the illusion of a continuous stream of information (Bregman, 1990; Warren, 1999). Conditions that foster this type of filling in have been identified in tactile (Kitagawa, Igarashi, & Kashino, 2009), visual (Komatsu, 2006), and auditory perception (King, 2007). In audition, the induc- tion of missing information can play a role in speech understanding (Bashford, Riener, & Warren, 1992; Shahin, Bishop, & Miller, 2009; Shinn-Cunningham & Wang, 2008) and has been studied because of its potential for providing information about the perceptual and neural mechanisms underlying auditory object formation. Early studies by Houtgast (1972) and Duifhuis (1980) used the continuity illusion in the form of pulsation thresholds to demonstrate psychophysical cor- relates of nonlinear frequency tuning in the auditory periphery, and later studies have examined the neural correlates of the continuity illusion at higher levels of the auditory system by using neuroimaging (Riecke et al., 2012; Riecke, van Opstal, Goebel, & Formisano, 2007; Shahin et al., 2009). The conditions under which the continuity illusion occurs have been studied since it was initially identified (Miller & Licklider, 1950). It is generally believed that the illusion occurs when the peripheral auditory response (e.g., auditory-nerve activity) produced by the interfering sound (or masker) overlaps completely with the response produced by the target sound (e.g., Duifhuis, 1980; Hout- gast, 1972; Petkov & Sutter, 2011; Warren, Obusek, & Ackroff, 1972). Our understanding of the conditions necessary for the illusion have been refined by recent studies, which have shown that the illusion can still occur under some circumstances in which the pe- ripheral auditory response provides evidence of the interruption, sug- gesting that masking of the interruption’s onset and offset are more critical than the ongoing portion (Haywood, Chang, & Ciocca, 2011) or that global features such as the specific loudness of the interferer play a more dominant role than the interferer’s fine-grained temporal structure (Riecke, Micheyl, & Oxenham, 2012). The physiological basis of the continuity illusion has also been studied using a wide range of electrophysiological techniques that have revealed important details of its generation and attentional requirements. Especially significant for this study is the finding by Micheyl et al. (2003), who used mismatched negativity (MMN) methods to show that physiological responses consistent with the continuity illusion do not seem to depend on focused attention. A similar finding was presented by Heinrich et al. (2011), who found that fMRI correlates of the continuity illusion seem to be indepen- dent of attention for complex vowel-like stimuli. These studies provide some neurophysiological evidence that the continuity illusion is represented neurally for both simple and complex sounds in a way that may not depend on directed atten- tion. Such findings would be strengthened through behavioral evidence that the continuity illusion effectively generates relevant auditory objects within attentionally demanding and complex acoustic environments (Gutschalk, Micheyl, & Oxenham, 2008; Jones, Macken, & Murray, 1993). To investigate the role of the continuity illusion in auditory mixtures, we used an auditory perceptual asymmetry identified by Cusack and Carlyon (2003), analogous to findings in the visual modality (e.g., Treisman & Gelade, 1980). Cusack and Carlyon This article was published Online First December 23, 2013. Dorea R. Ruggles and Andrew J. Oxenham, Department of Psychology, University of Minnesota. This research was supported by National Institutes of Health Grant R01 DC007657. Correspondence concerning this article should be addressed to Dorea R. Ruggles, Department of Psychology, University of Minnesota, Minneap- olis, MN 55455. E-mail: druggles@umn.edu T hi s do cu m en t is co py ri gh te d by th e A m er ic an Ps yc ho lo gi ca l A ss oc ia tio n or on e of its al lie d pu bl is he rs . T hi s ar tic le is in te nd ed so le ly fo r th e pe rs on al us e of th e in di vi du al us er an d is no t to be di ss em in at ed br oa dl y. Journal of Experimental Psychology: Human Perception and Performance © 2013 American Psychological Association 2014, Vol. 40, No. 3, 908–914 0096-1523/14/$12.00 DOI: 10.1037/a0035411 908 mailto:druggles@umn.edu http://dx.doi.org/10.1037/a0035411 (2003) found that long tones in mixtures of short tones were detected more easily than short tones in mixtures of long tones, and they attributed these asymmetries to the existence of feature- specific neurons tuned to longer rather than shorter durations. We asked whether an illusory long tone, composed of two short tones interrupted by a noise burst, would be detected if it were embedded in a complex pattern of similar but noncontiguous short tones and noise bursts. The question of whether illusory long tones evoke the same feature mapping and detection asymmetries as actual long tones has the potential to contribute to a deeper understanding of the continuity illusion and the processes of fea- ture coding and selection in complex acoustic environments. If the results show that the illusion is not detectable in complex mixtures of tones and noises and produces no perceptual asymmetries, we may conclude that the continuity illusion, as measured behavior- ally, stems from processes that are secondary to the feature map- ping that results in auditory asymmetry and is thus unlikely to play an important role in object formation in complex acoustic envi- ronments. In contrast, if listeners are able to detect illusory long tones in mixtures of tones and noise and display a perceptual asymmetry similar to that found for physical long tones, it would suggest that the continuity illusion is formed prior to or in con- junction with the feature mapping associated with perceptual asymmetries and therefore could play a crucial role in parsing complex auditory scenes. Experiment 1 Method The experiment tested listeners’ ability to detect illusory long tones elicited by a continuity illusion when the target tones were embedded in clouds of distracting tones and noises. Five condi- tions were studied (see Figure 1). In all conditions, short and long tones had total durations of 100 ms and 300 ms, respectively. All the noise bursts had total durations of 100 ms. Raised-cosine onset and offset ramps were applied to the first and last 10 ms of the tone and noise bursts. Pure-tone frequencies were randomly selected from 1/3 octave ranges centered at 315, 500, 800, 1250, 2000, and 3150 Hz with uniform distribution, and the noise bursts were filtered into the same 1/3 octave bands by 26th order Butterworth filters centered at the same frequencies. Empty 1/3 octave bands separated each of the bands to reduce spectral interactions between neighboring tones and noises. Each cloud was 2 s in duration and was constructed indepen- dently so that the timing, tone frequencies, and tone levels were unique for every presentation. The number of tones and noises was set for the target and nontarget bands in each condition and was equal in all nontarget bands, resulting in a predefined number of tones and noises evenly distributed among the frequency bands. In conditions without noise bursts, there were an equivalent of 36 100-ms tone units (including target constructions), equally distrib- uted across the six frequency bands. In conditions with noise bursts, there were an equivalent of 20 100-ms tone units and seven 100-ms noise units (including target constructions), distributed so that the five nontarget bands were all equal, but the target band was slightly different because of the target constructions. Each cloud was constructed by first randomly selecting the target frequency band and then randomly determining the different presentation frequencies for the tones in each band. After gener- ating the tone and noise bursts for the cloud, a unique initial onset time was determined for the target band by randomly selecting a delay between 100 ms and 200 ms. Tones and noises in each band were uniquely ordered and separated by random lengths of silence. The longest possible length for within-band interburst silences was calculated as the total silence in the band divided by the number of events in that band, and the minimum length was one quarter of the maximum length. The target could occur at any time after the first 100 ms and before the last 100 ms of the interval. The levels of the distracting tones were set based on a Gaussian distribution with a mean of 45 dB SPL and standard deviation of 2 dB, and noise bursts were set at 75 dB SPL. Target tones were presented at 40 dB SPL. The first condition required listeners to detect a long tone (LT) within a cloud of short tones. The second condition was the same, but the distracting clouds also included noise bursts (LTn). In the third condition, listeners were asked to detect a long tone in mixtures of short tones and noise bursts (ILTn), but in this case, no physical long tone was present; instead an illusory long tone was created by concatenating a short tone, a noise burst, and a second short tone at the same frequency to produce a tone-noise-tone sequence (onset and offset ramps overlapped at their half- amplitude points). The fourth condition required listeners to detect short tones (ST) in clouds of long tones, and the fifth condition Figure 1. Five conditions were tested. Random-frequency distractors, or “clouds,” in Conditions 1 (long tone [LT]) and 2 (long tone with noise [LTn]) consisted of short tones (ST) and, in the case of Condition 2, short noise bursts; the target tone in these clouds was a physical long tone. Clouds in Condition 3 (illusory long tone with noise [ILTn]) were made of short tones and noise, and targets were illusory