inherent bias for consonant intervals may well be linked to the perva-
siveness of octaves (2:1 ratio),perfect fifths (3:2 ratio),and perfect
fourths (4:3 ratio),all of which are perfect consonances in musical
systems the world over (Sachs 1943;Kolinski 1967).In contrast,this bias
is inconsistent with claims that musical consonance is primarily a matter
of convention (Serafine 1983;Blacking 1992).Indeed,the near absence
of small-integer ratios or “natural”melodic and harmonic intervals in
contemporary atonal music may contribute to its inaccessibility for most
untrained listeners and,therefore,its relegation to elite milieus (Meyer
1994;Schellenberg and Trehub 1996b).Small-integer ratios may function
as perceptual anchors,facilitating the encoding and retention of melodies
and,consequently,detection of subtle variations (Schellenberg and
Trehub 1996a,b).In short,the priority of small-integer over large-integer
frequency ratios can be considered another processing universal.Scale Structure
Another domain that is related only to music is the set of pitches in
musical scales.Scales,as formalizations of the pitches that occur in
melodies of a particular style,indicate the conventional means of filling
an octave interval with intermediate pitches.Despite considerable vari-
ability in scale structure across cultures,a number of similarities are
evident.For example,the typical division of the octave into five to seven
different pitches likely originates in cognitive constraints (Dowling and
Harwood 1986).Specific intervals tend to predominate,notably those
with small-integer ratios.Moreover,non-Western as well as Western
scales incorporate variations in step size as a general rule (Sloboda 1985).
The Western major scale consists of seven steps that are either two semi-
tones in size,as in doh-re,or one semitone,as in ti-doh(figure 23.4);the
harmonic minor scale has a contrasting sequence of unequal steps.
Pentatonic scales (five tones per octave) date from at least 2000 b.c.
(Kennedy 1994) and feature unequal step sizes.Although the music of
Thailand is thought to be based on an equal-step scale (Meyers-Moro
1993),Morton’s (1976) comprehensive analysis of the traditional Thai
repertoire yielded a pentatonic scale.(Some challenges of scale specifi-
cation in different cultures are described in Arom,Léothaud,and Voisin
1997.)
Unequal-step scales are thought to confer processing advantages,such
as allowing different tones to assume distinctive functions (Balzano
1980),facilitating the perception of tension and resolution (Shepard
1982),and providing the listener with a sense of location within a melody
(Brown 1988;Butler 1989).If unequal-step scales are inherently easier433 Human Processing Predispositions