Adults generally enjoy consonant sounds like choirs in harmony.
Infants also show a preference for consonance over dissonance.
Zentner and Kagan (1996) found that four-month-old infants preferred melodies accompanied by consonant intervals (major and minor thirds) compared to dissonant intervals (minor seconds).
Trainor and Heinmiller (1998) extended these findings, showing that six-month-old infants preferred perfect fifths and octaves over tritones and minor ninths.
Infants also preferred a normal, consonant version of a Mozart minuet over an edited dissonant version.
Infants' preferences are more reliably observed with large differences in dissonance. Crowder, Reznick, and Rosenkrantz (1991) found no significant preference for major chords over minor chords, likely because the consonance difference is subtle.
The ability to differentiate consonance and dissonance is not unique to humans; however, the preference for consonance seems to be.
The reason for infants' predisposition to prefer consonant intervals is unclear.
Early preferences for consonance may explain the prevalence of consonant intervals in music across cultures. Humans can learn to appreciate dissonance, but start with a preference for consonance.
Pitch Relations
Sensitivity to consonance and dissonance allows differentiation of musical intervals based on harmoniousness.
Sensitivity to the precise size of intervals is crucial for music recognition.
Relative pitch, the relation between pitches, is fundamental to musical structure appreciation.
A melody like "Happy Birthday" is recognizable regardless of pitch register.
Familiar melodies are recognized by the relations among pitches, not the starting pitch or consonance/dissonance.
Infants initially notice melody contour, but develop sensitivity to precise melodic intervals.
Some pitch relations, like octaves and fifths, are more easily processed and remembered.
Sensitivity to relative pitch isn't uniform across all intervals.
Simultaneous vs. Sequential Intervals
Sensitivity to pitch relations is observed for simultaneous and sequential tones, but the processes differ.
Simultaneous intervals create consonance and dissonance, allowing differentiation by consonance degree.
However, categorizing simultaneous intervals can be difficult due to dissonance reducing discrimination.
Overlapping frequency components in simultaneous intervals can cause perceptual fusion, making it hard to distinguish individual notes.
Sequential intervals don't generate sensory dissonance or perceptual fusion because notes are separated in time.
Dissonant simultaneous intervals seem to sound dissonant when played sequentially, but the reason isn't clear.
Schellenberg and Trehub (1996b) found that six-month-old infants showed a processing advantage for sequentially presented fifths and fourths over tritones.
Infants detected changes in interval size for fifths and fourths, but not tritones, in a repeating pattern of pure tones.
Fourths and fifths are consonant intervals, which might suggest a processing advantage for consonant intervals, but consonance/dissonance are sensory effects of simultaneous tone combinations.
The study used melodic sequences, and the sensory effects of dissonance arise from complex tones.
The advantage was observed even with pure tones, avoiding sensory interactions among overtones.
Further Findings on Interval Processing
An advantage for processing fourths, fifths, and octaves appears to continue throughout development.
Schellenberg and Trehub (1996a) found that six-year-olds and adults could discriminate fourths, fifths, and octaves from tritones and other intervals more easily when the standard interval was a fourth, fifth, or octave.
Performance was poor when the standard interval was dissonant.
This suggests that stable memory representations are formed for octaves, fifths, and fourths, but not for dissonant intervals.
The results can't be interpreted purely as a processing advantage for consonant intervals, because the effects were observed for melodic materials and pure-tone intervals.
One possibility is that these intervals are familiar due to their frequency in Western melodies.
Another explanation is that familiarity with octaves, fifths, and fourths in simultaneous intervals (common chords) influences judgments of the same intervals presented melodically.
Processing advantages for simultaneous intervals might generalize to sequentially presented intervals.
Scale Structure
Most scales have differently sized steps between consecutive tones.
The major scale has intervals of one and two semitones.
The prevalence of scales with unequal steps raises the question of whether music is processed more easily with such scales.
Trehub, Schellenberg, and Kamenetsky (1999) tested adults and nine-month-old infants on their ability to process and remember three scales: the major scale (unequal steps), an equal-step scale (octave divided into seven equal steps), and an unfamiliar unequal-step scale (octave divided into 11 equal steps, then constructing a seven-tone scale with four two-step intervals and three one-step intervals).
Both age groups were tested on their ability to detect when the sixth scale step was displaced upward slightly.