Some of the more salient spectral cues that need to be considered include spectral edgecues (Kohlrausch et al., 1992),which would allow listeners to respond based on the lowest or highest frequency component inthe complex, as well as spectral centroid cues, which would allow listeners to respond basedon where the spectral energy is concentrated (Moore andMoore, 2003; Micheyl and Oxenham, 2004;Micheyl et al., 2012). To ensurethat listeners are not responding on the basis of spectral information, one standard controlin pitchexperiments is the use of missing fundamental complexes. The ability to discriminate thepitch of amissing fundamental complex demonstrates that a listener is integrating information across the spectruminto a pitchpercept as opposed to responding on the basis of the spectral components themselves.
While fewer studies have examined infant's pitch perception using the appropriate acoustic controls,their results are consistent with the idea that complex pitch perception develops veryearly in life. In several pioneering behavioral studies, Clarkson and colleagues showed thatinfants at 7 months of age can categorize complex tones by their missing fundamental frequency (Clarkson and Rogers, 1995; Montgomery and Clarkson, 1997). Although, one electrophysiological investigationconducted in younger infants found that 3-month-olds do not show a cortical response tomissing fundamental pitch (He and Trainor, 2009), Lau and Werner (2012, 2014) found that both 3- and 7-month-olds behaviorally discriminated betweenharmonic complexes on the basis of the missing fundamental in the face of spectral changesresulting from varying harmonic composition. One limitation of these studies however, isthat it is difficult to confirm that nonverbal infants actually perceivedpitch. Thepresent study was conducted to address this limitation.
Although there have been no previous studies investigating infants' ability toperceivemelodies composed ofmissing fundamental complexes, many studies conducted with pure tones have shown thatinfants can detect changes in melodies on the basis of contour, intervals, and rhythm (Trehub et al., 1985; Trainor and Trehub, 1992; Hannon and Trehub, 2005). The question addressed in this study was whether theycan detect changes in melodies composed of missing fundamental harmonic complexes. Listenerslearned to respond when the melodic contour of a repeating standard melody changed and to ignorespectral variation that did not change the melodic contour. If infants are able to detect such amelodic violation,it strengthens the argument that these tones are eliciting a sense of musical pitch in infants. Withthat rationale, 3-month-olds, 7-month-olds, and adults were tested on a melodydiscrimination taskin which missing fundamental complexes carried the melody.
All participants were tested in one 60-min visit to the laboratory. The study consistedof one demonstration phase and one criterion phase. During the demonstration phase, theprobability of a change trial was 0.80. The reinforcer was activated after every changetrial regardless of the experimenter's response because the purpose of the demonstrationphase was to demonstrate the association between the reinforcer and the target, thechange melody,to the participant. The experimenter had to respond correctly on 4 of the last 5 changetrials and 1 no-change trial within a maximum of 15 trials to complete the demonstrationphase and progress to the criterion phase. All infants tested reached criterion in thedemonstration phase in the first session attempted. However, four adults required asecond attempt to complete the demonstration phase. No more than two attempted sessionswere permitted in the demonstration phase.
The test procedure, as well as the demonstration and criterion phases, were the same asin experiment I. The primary difference in the second experiment was that there were 15melodiesbelonging to 3 keys in each of the background and change stimulus sets as opposed to 5of each in a single key. For each presentation, the computer randomly selected 1 of the15 background or change melodies. As in experiment I, each note within a singlesequence was still composed of a different set of harmonics, so itwould sound as if a different musical instrument played each note. The key from onemelody to thenext, however, could change depending on which melody was selected. Ifparticipants perceived the melodic contour, the three transpositions would be equivalent and thetask would therefore be the same as in experiment I, to discriminate when a violation ofthe melodyoccurred. Listeners responding on the basis of absolute pitch would notreach criterion in the task.
A number of previous studies have demonstrated missing fundamental pitch perception in infantsbetween 3 and 7 months of age in the context of a constant pitch background (Clarkson and Rogers, 1995; Montgomery and Clarkson, 1997; Lau and Werner,2012, 2014). In Lau and Werner (2012, 2014),3-month-old infants were presented with spectrally varying complex tones and were required torespond whenever they heard a change in pitch against a background of repeated presentationsof one standard pitch. The current study extends those findings to the situation in whichthe pitchchange occurs in the context of both spectral and pitch variations.
Because both absolute and relative pitchinformation wasavailable in experiment I, it is possible that infants relied on absolute pitch cues to performthe task. In experiment II however, the use of relative pitch cues was required toperceive thetranspositions of the melody as equivalent. Saffran and colleagues have shown that whetherinfants discriminate on the basis of absolute versus relative pitch cues can beinfluenced by the structure of the task (Saffran andGriepentrog, 2001; Saffran, 2003; Saffran et al., 2005). When infants andadults were presented with a pitchsequencecontaining both types of cues, adults used the relative pitch cues while infantsused absolute pitchcues (Saffran and Griepentrog, 2001; Saffran, 2003). However, in a subsequent task with theabsolute pitchcues removed, infants also discriminated the pitchsequenceusing relative pitch cues like adults (Saffranet al., 2005). The results of the current study are, therefore,consistent with Saffran's work.
Infants' success on these experiments is also consistent with past melodydiscriminationstudies conducted with pure tones. In a task similar to the one used in the current study, Trehub et al. (1985) showed that 6- to8-month-olds were able to detect a change in a six-note melody, no matter the position atwhich the change occurred. Similarly, Trehub etal. (1984) presented 8- to 10-month-old infants melodies in transposition andfound that the transposition did not disrupt their ability to discriminate themelodies, as inexperiment II here. While these comparable results suggest that infant pure tonemelodydiscriminationabilities may generalize to complex tones, future investigations with different stimulusmanipulations and different tasks are required to further explore the relationship betweenpure tonepitch andcomplex pitchin infants.
Detectives have been investigating \"non-stop\" since becoming aware that Harmony was missing, the department added. They are working in conjunction with DCYF and the National Center for Missing and Exploited Children. The FBI has also joined the investigation.
Aldenberg said investigators have spoken with \"many family members,\" but wouldn't reveal whether that included her parents or who it was that reported her as missing. He said the last time she was enrolled in school was in Massachusetts.
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