inherently easier to encode than are tritones. No doubt, the inherent ease of processing
consonant intervals has contributed to their prominence in most musical systems.50,75,76
Historical and cross-cultural records document the inequality of intervals, with numerous
references to the beauty of octaves,perfect fifths, and perfect fourths77,78and the ugliness of
the tritone—‘the devil in music’in medieval times.^79
Not only do consonant intervals promote ease of processing, they also influence infant
attention and affect. For example, infants are more attentive and exhibit more positive
affect when listening to consonant music than to music with many dissonant intervals.^80 –^82
In principle, these preferences could arise from the predominance of consonant intervals
in the infant’s environment (e.g. speech, music, environmental sounds). In the absence of
such environmental input, as is the case for newborn infants whose deaf parents commu-
nicate by means of sign language, a similar pattern of preferences is evident.^83
Processing of scale structure
Scales across cultures are diverse, but they exhibit some common features. For example, the
octave is typically divided into five to seven discrete pitches, a design feature that is often
attributed to cognitive constraints.^84 Another similarity is the ubiquitous perfect fifth,
which is associated with enhanced processing in listeners of all ages.72,74,85Scales, for the
most part, have unequal steps^86 —for example, one- and two-semitone steps in diatonic
scales—a feature that is thought to confer processing advantages.87,88
To evaluate potential processing advantages of equal steps in scales, Trehub et al.^70
presented 9-month-old infants and adults with one of three ascending–descending scales:
(1) the major scale, which is highly familiar to adults and potentially familiar to infants,
(2) an artificial analogue of the major scale that was created by dividing the octave into
11 equal units, and selecting a seven-tone subset (featuring 1- and 2-unit steps), and
(3) an artificial equal-step scale that was created by dividing the octave into seven equal
steps.89,90These scales are depicted in Figure 1.2. Infants and adults were required to detect
a mistuned tone (0.75- and 0.5-semitone change for infants and adults, respectively) in the
comparison pattern. Adults’performance was highly accurate on the familiar major scale
and equally poor on the two unfamiliar scales. By contrast, scales with unequal steps, major
or artificial, enhanced infant performance relative to their performance on the equal-step
scale (see Figure 1.3). Thus, unequal-step scales, which are universal or near-universal,
facilitate musical pitch processing in infancy.
Infants’performance cannot be attributed to familiarity. It is possible, although highly
unlikely, that infants heard adults or siblings practising the major scale, but they could not
have heard the invented unequal-step scale that generated similar performance. By exten-
sion, other instances of enhanced processing—small-integer ratios, for example—are
unlikely to stem from exposure. Adults’performance is informative in revealing how
culture-specific experience, such as long-term exposure to the major scale, can override
inherent processing biases (e.g. advantages of unequal-step scales in general).
There are other examples of culture-specific exposure attenuating or eliminating initial
processing biases. For example, pitch processing in infancy is enhanced when the standard
and comparison patterns are presented in related keys—specifically, keys standing in a 3 : 2
ratio—rather than unrelated keys.^66 For adults, such enhancement is limited to melodies that
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