The Overlap of Dissociative Identity Disorder and Narcissistic Features in an Adolescent: A Case Report.

Understanding how different combinations of sounds affect our perceptual experience of music has long been a central goal in the cognitive sciences of music. At its core, this endeavor seeks to uncover how the foundational elements of musical language combine into patterns that elicit significantly different perceptual effects on listeners. This question has often been translated in psychoacoustic terms in order to assess the effect of specific acoustic qualities of sounds, such as timbre and pitch contour, on listeners [, ]. Two key areas in which this question has been thoroughly explored are harmony/melody and rhythm, with research in each domain offering critical insights into how the auditory system processes sound structures, from isolated intervals/chords to complex musical excerpts [, ]. A central construct governing the combination of sounds in the harmonic and melodic domains is the distinction between consonance and dissonance [, ]. These terms refer to the perceptual qualities that emerge when two tones are played either simultaneously (harmony) or in succession (melody). Consonances are typically defined as perceptually smooth, stable, and pleasant, whereas dissonances are often associated with rough, tense, or unpleasant sensations [, , , , ]. This dichotomy has played a foundational role in the development of Western musical theory and composition, influencing how chords and intervals are combined into complex musical structures []. Since the first theorization by Pythagoras, consonance and dissonance have often been explained in terms of frequency ratios, with more consonant intervals being expressed by low‐order frequency ratios, and more dissonant by more complex ones []. For example, intervals such as the octave (2:1) or perfect fifth (3:2) are typically judged as highly consonant, while combinations of sounds whose frequency can be expressed by ratios such as 16:9 or 65:50 result in more dissonant intervals (though see [] for an anti‐Pythagorean perspective). Parallel to this, research has delved into rhythm perception by examining how listeners perceive and respond to rhythmic streams with different structures, from isochronous two‐beat patterns to the simultaneous combination of different streams, commonly referred to as polyrhythms [, , ]. Interestingly, a robust body of empirical research demonstrates that rhythmic sequences with temporally spaced events conforming to simple integer ratios (e.g., 2:3, with inter‐onset intervals of 200 and 300 ms) tend to be more easily perceived, reproduced, and remembered than those that are based on more complex relationships (e.g., 2.5:3, with inter‐onset intervals of 250 and 300 ms) [, , , , ].