The survey of musical material in appendix 3.05 gives an overview of musical material presented in
the papers at the three conferences. The number of conference papers is as follows: NM I: 61, NM
II: 53, NM III: 79, a total of 193 papers. In order to permit comparison of applied material, appendix
3.05 shows a selection of papers that use artificial stimuli, acoustic sounds, and recorded music.
Estimation of ecological validity
Source not indicated
32 papers out of 193 do not indicate the source of the stimulus material. This lack of information ob-
scures the validity of the research in question.
Sinus tones
23 studies apply sinus tones as stimuli. Some of these studies have chosen sinus tones in order to
ensure strict experimental control. Other studies investigate differences in neural perception of sinus
tones and musical tones. The results of a number of studies show clear differences between percep-
tion of sinus tones and perception of musical tones, suggesting that the use of sinus tones as stimuli
may reduce the ecological validity of an experiment.
Synthesized material
46 studies apply synthesized material as stimuli. Some of these studies are based on the precise
manipulation of sound spectra, which is only possible in synthesized material. Other studies report
the use of synthesized instrumental timbres, which approximate the features of acoustic sounds.
Nevertheless, the properties of synthesized sounds are not equal to the properties of acoustic
sounds. Synthesized sounds do not emulate the minute spectral and temporal variations that are
important for the perception and emotional impact of natural sounds. This problem is not discussed
in the studies. Thus, the ecological validity of studies based on synthesized sound remains question-
able.
Future research can benefit from current investigations which clarify differences between synthe-
sized tones and acoustic tones; research into the modulations and microtemporal evolutions of
sound spectra (Malone & Schreiner 2010:125-148), and research into the processing of differences
between auditory information from the two ears^25 (Yin & Kuwada 2010:271-302).
Acoustic stimuli
18 studies apply acoustic stimuli.
11 studies apply tones of acoustic instruments, three in NM I, one in NM II, and seven in NM III.
7 studies report the use of singing voice, 0 in NM I, three in NM II, and four in NM III.
The scarcity of acoustic stimuli is apparent. One may speculate whether it is the judgment of neuro-
scientists that the use of acoustic stimuli implies an unacceptable reduction of experimental control.
Percussion music is totally absent from the conference papers, with the exception of a few
drum patterns in tapping studies. The multifaceted timbres and multivariable rhythms of percussive
music constitute a rich unexplored field of study. Similarly, the expressive qualities of the singing
voice offer a rich material for future studies.
Recorded music
36 studies apply recordings of real music. In 19 papers, the recorded music is specified. Noteworthy
papers which apply specified recorded music are the following:
25 The auditory system detects minute differences in timing between the two ears, due to the fact that sound from one
side arrives earlier in one of the ears. The auditory system also detects minute differences in sound level between the
ears. The technical terms are interaural time disparities (ITD) and interaural level disparities (ILD)