Auditory Illusion Research Articles

Cats exhibit the Franssen Effect illusion

The Franssen Effect (FE) is a striking auditory illusion previously demonstrated only in humans. To elicit the FE, subjects are presented with two spatially-separated sounds; one a transient tone with an abrupt onset and immediate ramped offset and the other a sustained tone of the same frequency with a ramped onset which remains on for several hundred ms. The FE illusion occurs when listeners localize the tones at the location of the transient signal, even though that sound has ended and the sustained one is still present. The FE illusion occurs most readily in reverberant environments and with pure tones of approximately 1-2.5 kHz in humans, conditions where sound localization is difficult in humans. Here, we demonstrate this illusion in domestic cats using, for the first time, localization procedures. Previous studies in humans employed discrimination procedures, making it difficult to link the FE to sound localization mechanisms. The frequencies for eliciting the FE in cats were higher than in humans, corresponding to frequencies where cats have difficulty localizing pure tones. These findings strengthen the hypothesis that difficulty in accurately localizing sounds is the basis for the FE.

Neural Correlates of the Precedence Effect in the Inferior Colliculus of Behaving Cats

Several auditory spatial illusions, collectively called the precedence effect (PE), occur when transient sounds are presented from two different spatial locations but separated in time by an interstimulus delay (ISD). For ISDs in the range of localization dominance (<10 ms), a single fused sound is typically located near the leading source location only, as if the location of the lagging source were suppressed. For longer ISDs, both the leading and lagging sources can be heard and localized, and the shortest ISD where this occurs is called the echo threshold. Previous physiological studies of the extracellular responses of single neurons in the inferior colliculus (IC) of anesthetized cats and unanesthetized rabbits with sounds known to elicit the PE have shown correlates of these phenomena though there were differences in the physiologically measured echo thresholds. Here we recorded in the IC of awake, behaving cats using stimuli that we have shown to evoke behavioral responses that are consistent with the precedence effect. For small ISDs, responses to the lag were reduced or eliminated consistent with psychophysical data showing that sound localization is based on the leading source. At longer ISDs, the responses to the lagging source recovered at ISDs comparable to psychophysically measured echo thresholds. Thus it appears that anesthesia, and not species differences, accounts for the discrepancies in the earlier studies.

Quantifying the auditory saltation illusion: an objective psychophysical methodology.

Under conditions of rapid presentation, brief acoustic stimuli repeatedly delivered first at one location, then at another, are systematically mislocalized, with stimuli perceived as traveling smoothly between the two locations. This robust illusory motion percept is termed "auditory saltation." Currently, the characteristics and mechanisms of auditory saltation are not well understood. The lack of objective methods capable of quantifying the illusion on an individual basis seems a limiting factor for this area of research. In this study, we outline an objective psychophysical task that estimates the interstimulus interval at which the saltation illusion is reliably distinguishable from simulated motion. Experiment 1 examined the psychophysical function relating task performance to ISI and addressed the suitability of the task for use with adaptive psychophysical procedures. Experiment 2 directly compared performance on the task with that of another quantification method. The results suggested that this objective approach to the study of auditory saltation overcomes difficulties associated with more subjective methods, and provides a reliable paradigm within which to quantify the temporal parameters of saltation on an individual basis.

Factors influencing audiovisual fission and fusion illusions

Information processing in auditory and visual modalities interacts in many circumstances. Spatially and temporally coincident acoustic and visual information are often bound together to form multisensory percepts [B.E. Stein, M.A. Meredith, The Merging of the Senses, A Bradford Book, Cambridge, MA, (1993), 211 pp.; Psychol. Bull. 88 (1980) 638]. Shams et al. recently reported a multisensory fission illusion where a single flash is perceived as two flashes when two rapid tone beeps are presented concurrently [Nature 408 (2000) 788; Cogn. Brain Res. 14 (2002) 147]. The absence of a fusion illusion, where two flashes would fuse to one when accompanied by one beep, indicated a perceptual rather than cognitive nature of the illusion. Here we report both fusion and fission illusions using stimuli very similar to those used by Shams et al. By instructing subjects to count beeps rather than flashes and decreasing the sound intensity to near threshold, we also created a corresponding visually induced auditory illusion. We discuss our results in light of four hypotheses of multisensory integration, each advocating a condition for modality dominance. According to the discontinuity hypothesis [Cogn. Brain Res. 14 (2002) 147], the modality in which stimulation is discontinuous dominates. The modality appropriateness hypothesis [Psychol. Bull. 88 (1980) 638] states that the modality more appropriate for the task at hand dominates. The information reliability hypothesis [J.-L. Schwartz, J. Robert-Ribes, P. Escudier, Ten years after Summerfield: a taxonomy of models for audio-visual fusion in speech perception. In: R. Campbell (Ed.), Hearing by Eye: The Psychology of Lipreading, Lawrence Earlbaum Associates, Hove, UK, (1998), pp. 3–51] claims that the modality providing more reliable information dominates. In strong forms, none of these three hypotheses applies to our data. We re-state the hypotheses in weak forms so that discontinuity, modality appropriateness and information reliability are factors which increase a modality's tendency to dominate. All these factors are important in explaining our data. Finally, we interpret the effect of instructions in light of the directed attention hypothesis which states that the attended modality is dominant [Psychol. Bull. 88 (1980) 638].

Mechanisms underlying the auditory continuity illusion

This study investigates the auditory continuity illusion, combining psychophysics and magnetoencephalography. Stimuli consisted of amplitude-modulated (AM) noise interrupted by bursts of louder, unmodulated noise. Subjective judgments confirmed that the AM was perceived as continuous, a case of illusory continuity. Psychophysical measurements showed that the illusory modulation had little effect on the detection of a physical modulation, i.e., the illusory modulation produced no modulation masking. Duration discrimination thresholds for the AM noise segments, however, were elevated by the illusion. A whole-head magnetoencephalographic system was used to record brain activity when listeners attended passively to the stimuli. The AM noise produced a modulated magnetic activity, the auditory steady-state response. The illusory modulation did not produce such a response, instead, a possible neural correlate of the illusion was found in transient evoked responses. When the AM was interrupted by silence, oscillatory activity in the gamma-band range as well as slow evoked potentials were observed at each AM onset. In the case of the illusion, these neural responses were largely reduced. Both sets of results are inconsistent with a restoration of the modulation in the case of illusory continuity. Rather, they point to a role for onset-detection mechanisms in auditory scene analysis.

ARTSTREAM: a neural network model of auditory scene analysis and source segregation

Multiple sound sources often contain harmonics that overlap and may be degraded by environmental noise. The auditory system is capable of teasing apart these sources into distinct mental objects, or streams. Such an ‘auditory scene analysis’ enables the brain to solve the cocktail party problem. A neural network model of auditory scene analysis, called the ARTSTREAM model, is presented to propose how the brain accomplishes this feat. The model clarifies how the frequency components that correspond to a given acoustic source may be coherently grouped together into a distinct stream based on pitch and spatial location cues. The model also clarifies how multiple streams may be distinguished and separated by the brain. Streams are formed as spectral-pitch resonances that emerge through feedback interactions between frequency-specific spectral representations of a sound source and its pitch. First, the model transforms a sound into a spatial pattern of frequency-specific activation across a spectral stream layer. The sound has multiple parallel representations at this layer. A sound's spectral representation activates a bottom-up filter that is sensitive to the harmonics of the sound's pitch. This filter activates a pitch category which, in turn, activates a top-down expectation that is also sensitive to the harmonics of the pitch. Resonance develops when the spectral and pitch representations mutually reinforce one another. Resonance provides the coherence that allows one voice or instrument to be tracked through a noisy multiple source environment. Spectral components are suppressed if they do not match harmonics of the top-down expectation that is read-out by the selected pitch, thereby allowing another stream to capture these components, as in the ‘old-plus-new heuristic’ of Bregman. Multiple simultaneously occurring spectral-pitch resonances can hereby emerge. These resonance and matching mechanisms are specialized versions of Adaptive Resonance Theory, or ART, which clarifies how pitch representations can self-organize during learning of harmonic bottom-up filters and top-down expectations. The model also clarifies how spatial location cues can help to disambiguate two sources with similar spectral cues. Data are simulated from psychophysical grouping experiments, such as how a tone sweeping upwards in frequency creates a bounce percept by grouping with a downward sweeping tone due to proximity in frequency, even if noise replaces the tones at their intersection point. Illusory auditory percepts are also simulated, such as the auditory continuity illusion of a tone continuing through a noise burst even if the tone is not present during the noise, and the scale illusion of Deutsch whereby downward and upward scales presented alternately to the two ears are regrouped based on frequency proximity, leading to a bounce percept. Since related sorts of resonances have been used to quantitatively simulate psychophysical data about speech perception, the model strengthens the hypothesis that ART-like mechanisms are used at multiple levels of the auditory system. Proposals for developing the model to explain more complex streaming data are also provided.

Physical Basis of Interference Effects in Hearing

To capture faint sounds, the ear uses an active system of amplification. We and our colleagues have put forward the idea that the amplifier comprises a set of ‘self-tuned critical oscillators’: each hair cell contains a force-generating dynamical system which is maintained at the threshold of an oscillatory instability, or Hopf bifurcation. The active response to a pure tone is perfectly suited to the ear’s needs, since it provides frequency selectivity, exquisite sensitivity and wide dynamic range. However, the intrinsic nonlinearity of the mechanism causes tones of different frequency to interfere with one another in the cochlea. In order to provide a framework for understanding how the ear processes the more complex sounds of speech and music, we have examined the response of a critical Hopf oscillator to two tones. Our calculations indicate how the response to one tone is suppressed by the presence of a second tone of similar frequency. They also show how a characteristic spectrum of distortion products is generated. The results are in accord with experimental observations of basilar membrane motion. Given the complexity of the nonlinear response, how does the ear distinguish the frequency components of a sound source? We propose a simple model of pitch extraction based on the timings of neural spikes, and investigate to what extent psychophysical phenomena such as the sensation of dissonance and auditory illusions can be attributed to the physical nature of the peripheral detection apparatus.

The Neurophysiological Basis of the Auditory Continuity Illusion: A Mismatch Negativity Study

A sound turned off for a short moment can be perceived as continuous if the silent gap is filled with noise. The neural mechanisms underlying this "continuity illusion" were investigated using the mismatch negativity (MMN), an event-related potential reflecting the perception of a sudden change in an otherwise regular stimulus sequence. The MMN was recorded in four conditions using an oddball paradigm. The standards consisted of 500-Hz, 120-msec tone pips that were either physically continuous (Condition 1) or were interrupted by a 40-msec silent gap (Condition 2). The deviants consisted of the interrupted tone, but with the silent gap filled by a burst of bandpass-filtered noise. The noise either occupied the same frequency region as the tone and elicited the continuity illusion (Conditions 1a and 2a), or occupied a remote frequency region and did not elicit the illusion (Conditions 1b and 2b). We predicted that, if the continuity illusion is determined before MMN generation, then, other things being equal, the MMN should be larger in conditions where the deviants are perceived as continuous and the standards as interrupted or vice versa, than when both were perceived as continuous or both interrupted. Consistent with this prediction, we observed an interaction between standard type and noise frequency region, with the MMN being larger in Condition 1a than in Condition 1b, but smaller in Condition 2a than in Condition 2b. Because the subjects were instructed to ignore the tones and watch a silent movie during the recordings, the results indicate that the continuity illusion can occur outside the focus of attention. Furthermore, the latency of the MMN (less than approximately 200 msec postdeviance onset) places an upper limit on the stage of neural processing responsible for the illusion.

Psychophysical investigation of an auditory spatial illusion in cats: the precedence effect.

The precedence effect (PE) describes several spatial perceptual phenomena that occur when similar sounds are presented from two different locations and separated by a delay. The mechanisms that produce the effect are thought to be responsible for the ability to localize sounds in reverberant environments. Although the physiological bases for the PE have been studied, little is known about how these sounds are localized by species other than humans. Here we used the search coil technique to measure the eye positions of cats trained to saccade to the apparent locations of sounds. To study the PE, brief broadband stimuli were presented from two locations, with a delay between their onsets; the delayed sound meant to simulate a single reflection. Although the cats accurately localized single sources, the apparent locations of the paired sources depended on the delay. First, the cats exhibited summing localization, the perception of a "phantom" sound located between the sources, for delays < +/-400 micros for sources positioned in azimuth along the horizontal plane, but not for sources positioned in elevation along the sagittal plane. Second, consistent with localization dominance, for delays from 400 micros to about 10 ms, the cats oriented toward the leading source location only, with little influence of the lagging source, both for horizontally and vertically placed sources. Finally, the echo threshold was reached for delays >10 ms, where the cats first began to orient to the lagging source on some trials. These data reveal that cats experience the PE phenomena similarly to humans.

The Neurophysiological Basis of the Auditory Continuity Illusion: A Mismatch Negativity Study

Abstract A sound turned off for a short moment can be perceived as continuous if the silent gap is filled with noise. The neural mechanisms underlying this “continuity illusion” were investigated using the mismatch negativity (MMN), an eventrelated potential reflecting the perception of a sudden change in an otherwise regular stimulus sequence. The MMN was recorded in four conditions using an oddball paradigm. The standards consisted of 500-Hz, 120-msec tone pips that were either physically continuous (Condition 1) or were interrupted by a 40-msec silent gap (Condition 2). The deviants consisted of the interrupted tone, but with the silent gap filled by a burst of bandpass-filtered noise. The noise either occupied the same frequency region as the tone and elicited the continuity illusion (Conditions 1a and 2a), or occupied a remote frequency region and did not elicit the illusion (Conditions 1b and 2b). We predicted that, if the continuity illusion is determined before MMN generation, then, other things being equal, the MMN should be larger in conditions where the deviants are perceived as continuous and the standards as interrupted or vice versa, than when both were perceived as continuous or both interrupted. Consistent with this prediction, we observed an interaction between standard type and noise frequency region, with the MMN being larger in Condition 1a than in Condition 1b, but smaller in Condition 2a than in Condition 2b. Because the subjects were instructed to ignore the tones and watch a silent movie during the recordings, the results indicate that the continuity illusion can occur outside the focus of attention. Furthermore, the latency of the MMN (less than approximately 200 msec postdeviance onset) places an upper limit on the stage of neural processing responsible for the illusion.

Cocktails for Franssen: Asynchronous transient bias and other attentional factors in auditory localization

The cocktail-party paradigm was applied to nonspeech signals. Pure-tone stimuli were used in an extension of the Franssen effect, an auditory illusion wherein the location of a slow-onset signal is perceived to be the same as a simultaneous, contralateral sudden-onset signal. Listeners heard simultaneous sudden-onset (transient) and contralateral slow-onset (steady-state) tones in a reverberant environment with a second delayed transient from a third azimuthal location. Results showed that the Franssen effect was either maintained or ‘‘reset,’’ but not reduced. The ongoing steady-state tone was perceived either at the initial-transient and then delayed-transient location, or at the initial transient location only. None of the listeners showed a location bias to the delayed transient tone when its frequency differed from the initial signal frequency or was replaced with noise. In additional conditions based on the ‘‘false Haas effect,’’ consonant–vowel pairs representing transient and steady-state signals were segregated contralaterally in a reverberant space. Results showed no resemblance to the Franssen effect. In general, results indicated that the role of attention is fundamental to the localization of an ongoing stimulus. [Work supported by NIH.]

INFLUENCE OF THE SUPPRESSION OF SELF-DISCREPANT THOUGHTS ON THE VIVIDNESS OF PERCEP TION OF AUDITORY ILLUSIONS

Based on the relationship between cognitive intrusions and auditory hallucinations established by Morrison and Baker (2000) and Morrison, Haddock and Tarrier (1995) the present study examines the possible effect of the repeated suppression of self-discrepant thoughts on the vividness of auditory illusions in a sample from a non-clinical population. Sixty-one participants were randomly assigned to a suppression of thoughts group (n = 31) or a focalization of thoughts group (n = 30) with different levels of self-discrepancy. After carrying out the task over a period of 48 hours, participants were presented with non-vocal auditory stimulation and asked to state whether they heard any verbalizations, and if so, how clearly. Results show how the repeated suppression of self-discrepant thoughts has a considerable effect on the vividness of illusions (F(1, 50) = 16.09; p &lt; 0.001). The implications of these results for psychological therapy are analysed, with special emphasis on the importance of a research line based on acceptance.

Changing words and changing sounds: A change of tune for verbal transformation theory?

The verbal transformation effect, an auditory illusion in which physically invariant repetitive verbal input undergoes perceptual transformation, has traditionally been interpreted as a speech-specific phenomenon. Experiment 1 showed that the effect is not limited to speech, but occurs in non-speech categories such as music and other complex everyday sounds, with transformations being comparable in nature and number to those in speech. Experiment 2 provided evidence for an alternative, broader-based view of the phenomenon, involving spreading activation through a multidimensional associative network of mental representations, by demonstrating that creating or activating pre-existing links between a single complex non-verbal stimulus and other representations by priming led to an increase in transformations.

The right hemisphere pitches in

In recent years, cognitive neuroscience has been making great efforts to home in on the difference between the physical stimulus and the perceived sensation, hence the attempts to find neural correlates of what we actually perceive. In auditory illusions, the pitch of a sound – its subjective highness or lowness – may not be the same as its physical frequency. In the missing frequency (MF) illusion, for example, people can hear frequencies not present in physical sound waves. Using MF stimuli and magnetoencephalography (MEG), Patel and Balaban recently showed that there is a correlation between the temporal pattern of brain activation in the right cerebral hemisphere and the subjectively perceived pitch [Nature Neurosci. (2001) 4, 839–844]. Using the fact that people differ in their susceptibility to the MF illusion, Patel and Balaban divided their subjects into those who perceived pitch change in the same direction as frequency change, and those who perceived it in the opposite direction. Comparing MEG scans from the two groups of subjects, they found that, although many areas of the brain respond to the stimulus of a frequency change, only areas in the right hemisphere code for change of subjective pitch. MW

Physical basis of two-tone interference in hearing.

The cochlea uses active amplification to capture faint sounds. It has been proposed that the amplifier comprises a set of self-tuned critical oscillators: each hair cell contains a force-generating dynamical system that is maintained at the threshold of an oscillatory instability, or Hopf bifurcation. While the active response to a pure tone provides frequency selectivity, exquisite sensitivity, and wide dynamic range, its intrinsic nonlinearity causes tones of different frequency to interfere with one another in the cochlea. Here we determine the response to two tones, which provides a framework for understanding how the ear processes the more complex sounds of speech and music. Our calculations of two-tone suppression and the spectrum of distortion products generated by a critical oscillator accord with experimental observations of basilar membrane motion and the nervous response. We discuss how the response of a set of self-tuned oscillators, covering a range of characteristic frequencies, represents the structure of a complex sound. The frequency components of the stimulus can be inferred from the timing of neural spikes elicited by the vibrating hair cells. Passive prefiltering by the basilar membrane improves pitch discrimination by reducing interference between tones. Our analysis provides a general framework for examining the relation between the physical nature of the peripheral detection apparatus and psychophysical phenomena such as the sensation of dissonance and auditory illusions.

Language Affects Sound Perception

At the 140th meeting of the Acoustical Society of America here last week, a psychologist demonstrated that an auditory illusion based on the tritone--two notes a half-octave apart played together--is perceived differently by listeners with different linguistic histories. And those perceptions might help psychologists understand how the brain rewires itself during childhood.

An auditory negative after-image as a human model of tinnitus

The Zwicker tone (ZT) is an auditory after-image, i.e. a tonal sensation that occurs following the presentation of notched noise. In the present study, the hypothesis that neural lateral inhibition is involved in the generation of this auditory illusion was investigated in humans through differences in perceptual detection thresholds measured following broadband noise, notched noise, and low-pass noise stimulation. The detection thresholds were measured using probe tones at several frequencies, within as well as outside the suppressed frequency range of the notched noise, and below as well as above the corner frequency of the low-pass noise. Thresholds measured after broadband noise using a sequence of four 130-ms probe tones (with a 130-ms inter-burst interval) proved to be significantly smaller that those measured using the same probe tones after notched noise at frequencies falling within the notch, but larger for frequencies on the outer edges of the noise. Thresholds measured following low-pass noise using the same sequence of probe tones were found to be smaller at frequencies slightly above the corner, but larger at lower, neighboring frequencies. This pattern of results is consistent with the hypothesis that the changes in auditory sensitivity induced by stimuli containing sharp spectral contrasts reflect lateral inhibition processes in the auditory system. The potential implications of these findings for the understanding of the mechanisms underlying the generation of auditory illusions like the ZT or tinnitus are discussed.

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.

Technetium-99m-ethyl cysteinate dimer brain perfusion loss in pediatric postictal psychosis

A 91/i-YEAR-OLD BOY was admitted to the hospital with status epilepticus and was treated with intravenous diazepam, phenytoin, and midazolam. After the convulsions stopped, he remained agitated and confused. Twenty-four hours later, psychotic ideation was noticed. He developed visual hallucinations, confused speech, auditory illusions, psychomotor restlessness, and disorganized behavior. His medical history was remarkable for a right hemiplegia diagnosed in the first year of life, caused by a polycythemia-related neonatal stroke. A brain computed tomography (CT) scan that was performed a year later showed an enlarged left ventricle and left hemispheric atrophy. At age 9, the patient was hospitalized for prolonged left-sided complex partial seizures, followed by Todd's paralysis on the right side. The neurological examination on the current admission revealed mild right hemiparesis, unchanged from before. Routine serum biochemistry and a complete blood count were normal. A lumbar puncture was normal. Repeated electroencephalograms (EEGs) showed left-sided slowing but no epileptic activity. A brain magnetic resonance imaging (MRI) scan showed severe atrophy of the left hemisphere with a thalamic hypodensity (Fig 1), similar to the previous imaging. The patient was diagnosed with postictal schizophrenia-like psychosis. A perfusion brain single photon emission computed tomography (SPECT) was performed 30 minutes after injecting 12 mCi (444 MBq) of Technetium (Tc)-99m-ethyl cysteinate dimer (ECD) intravenously by using a dualhead gamma camera. The images showed markedly decreased perfusion to the left hemisphere, including the basal ganglia and the thalamus (Fig 2A). The hypoperfusion was most prominent in the left medial temporal lobe. Moderately diminished perfusion was also observed in the frontal lobes. The psychosis lasted for 7 days and resolved gradually without treatment. A repeat SPECT study 3 months later (Fig 2B) showed improved perfusion to the left temporal lobe and to the fight frontal lobe. The patient remained asymptomatic after a 6-month follow-up. Brief psychotic episodes may follow a bout of seizure clusters or a recent exacerbation in seizure frequency. 17 Postictal psychosis may develop in nearly 10% of adult patients, 6 but it is rare in children. The psychosis may be caused by repeated electrical discharges that change local neurotransmitter activity. It is also conceivable that structural brain abnormalities, eg, cortical dysgenesis or diffuse brain lesions, may lead to both the epilepsy and the psychosis. Postictal psychosis usually resolves within a few days. 5 Recurrent seizures may exacerbate the psychosis, and careful monitoring of anticonvulsant therapy is mandatory. EEG abnormalities persist in the majority of patients during the psychosis. 1 Some suggested risk factors are early onset and severe epilepsy, secondary generalization of seizures, certain anticonvulsive drugs, and temporal lobectomy. Most investigators suggest that psychosis in epilepsy is preferentially associated with temporal lobe seizures. 8-a2 MRI studies show that postictal psychosis is most likely to occur in patients with resistant temporal lobe epilepsy stemming from mesial temporal sclerosis, especially on the left side. 6 Changes in postsynaptic dopamine receptor sensitivity have been suggested as the mediating mechanism. SPECT studies have shown low levels of striatal dopamine D2 receptors in patients with peri-ictal psychosis. 13 Possible differential diagnoses for our patient are listed below.

Phoneme restoration in infants

In a classic study, Warren (1971) replaced the medial /s/ in legislatures with a cough, and found that adult listeners heard the word as being complete. This auditory illusion demonstrates effects of both bottom-up and top-down information: it occurs only when there is a possible masking noise (it does not occur if the /s/ is replaced with silence), and it occurs at least in part because of the listener’s knowledge that legislatures is a real word. Thus, it involves an interaction between multiple sources of information. The present study investigates whether infants will also show such an effect, and thus whether this interaction between levels of language processing is itself something which develops over time. Infants are shown videos of a cat and a dog in a preferential-looking paradigm, and hear the words kitty and doggie both in the clear, and with the medial stop consonant replaced by either noise or silence. Results examine whether infants will treat the words as whole (that is, match them to the appropriate referent) when the middle sound is replaced with noise as compared to when it is replaced with silence. [Work supported by NIH Grant R03 HD37822-01 to the University of Iowa.]