Introduction
The octave illusion was initially produced by the stimulus configuration that is depicted in Figure 1a. Here there two tones that are spaced an octave apart, which are then repeated in alternation. This sequence was presented to both ears simultaneously, however, when the right ear received the high tone, the left ear received the low tone and vice versa with each ear receiving opposite tones. This presents the listener with a single continuous two-tone chord, but the ear in which each input is received switches repeatedly (Deutsch, 1981).
This sequence provokes various illusions. The most common illusion that arises from this sequence is illustrated in Figure 1b. This shows a single tone switched from ear to ear, whose pitch simultaneously switched back and forth from high to low. Thus, the listeners heard a single high tone in one ear, which alternated with a single low tone in the other ear (Deutsch, 1981).
The illusion is tried further when various subjects attempt to alter the ear in which the high and low tones are perceived by simply reversing the headphones. Most people still hear exactly the same thing; that is, the tone that was received in the right ear is still perceived in the right ear and the tone that was received in the left ear is still perceived in the left ear. The listener originally associated the difference in right versus left ear perception to the earphone, but the reversal of the headphones proves to the listener that it is not the headphones, but indeed the ears that perceive the different tones. This percept is illustrated in Figure 2. Figure 2 provides a written report by someone with absolute pitch (Deutsch, 1981).
The octave illusion was shown to be based on two factors: (1) the perception of the frequencies presented to a single ear (those presented to the other ear being suppressed), and (2) the localization of each tone to the ear receiving the high frequency signal. This is regardless to whether the higher or lower frequency was actually perceived (Deutsch, 1974). More recently, the octave illusion is explained on the foundation of selective attention.
Selective attention is expressed as the ability to selectively attend to certain stimulus; blocking out unimportant stimulus. Selective attention also explains how an individual in a room full of people can focus on only one conversation. The auditory system contains many centrifugal pathways, which extend from the auditory cortex, Brodmann’s areas 41 and 42 (Andorn, 1989), through the medial geniculate body, colliculi, olivary regions, and back to cochlea. Some of these structures are proposed to play a role in selective attention by modulating midbrain and auditory nerve responses or possibly the activity of the cochlear hair cells (Chambers, 2002).
In general, it was found that among the right-handers who obtained the percept that there was a single high tone in one ear, which alternated with a single low tone in the other ear, had a highly significant tendency to hear the higher tone on the right and the lower tone on the left. This observation did not hold true for left-handers (Deutsch, 1974). This is in accordance with the literature showing that although most right-handers have clear left-hemisphere dominance, the pattern of cerebral dominance among left-handers varies considerably (Deutsch, 2009). This helps explain why the proportion of listeners obtaining complex percepts was much higher in left-handers than in the right-handers (Deutsch, 1981). Furthermore, these results are consistent with neurological evidence.
Neurological evidence suggests that the majority of right-handers are left-hemisphere dominant; meaning their speech is represented in the left cerebral hemisphere. However, this is only true for approximately two-thirds of left-handers as opposed to the overwhelming majority of right-handers. The remaining one-third are right-hemisphere dominant, which means that although most left-handers have speech represented in the left cerebral hemisphere, a substantial amount of left-handers have speech in both hemispheres (Deutsch, 1981). The variation of the hemispheres may help account for the variation of tone localization that can be present in some left-handed populations. Since the brain exhibits contralateral tendencies, it would come as no surprise that right-handers would tend to strongly follow the information presented to their right side (the auditory cortex is on the left side of the brain; right-handed people have stronger pathways to the left hemisphere because of their right-handed dominance to the contralateral left hemisphere) (Deutsch, 1981).
The result of a substantial right-ear advantage for a sequence that is nonverbal is seemingly contradictory according to the widely held belief that the dominant hemisphere is used for verbal functions, while the non-dominant hemisphere is used for nonverbal or musical functions. Left-ear advantages have been obtained in dichotic listening tasks involving musical composition. Thus, it would then be the left ear that would perceive the higher tone in the sequence. Although, a left-ear dominance has been obtained for nonverbal sequences, right-ear advantages have also been obtained. It was found that when subjects were required to recognize two frequencies, dichotically, the ear advantage was purely right (Deutsch, 1981).
In short, this research in its current form focuses on repeating the octave illusion experiment. Based upon previous experiments, it is believed that the majority of right-handed subjects will perceive a high tone on the right alternating with a low tone on the left, while left-handed subjects will vary more in perception, but nonetheless, the majority of left-handed subjects will perceive a high tone on the left alternating with a low tone on the right. Additionally, musical training of the subjects will be assessed for a positive correlation in the ability to correctly establish the differences between the frequencies.
Methods
Of the right-handed participants, 14 were male (43.8%) and 18 were female (56.3%). From the left-handed participants, 7 participants were male (43.8%) and 9 were female (56.3%).
Furthermore, it was noted whether these 51 students had musical training, which was defined at three years or more learning or playing a musical instrument (Deutsch, 1981). 23 students did not have musical training (45.1%), while the remaining 28 students responded as having musical training (54.9%).
Each subject was tested individually. They were explained that they would hear a sequence of tones that would repeat. Upon the conclusion of the tones they were asked to indicate on a forced choice questionnaire which description best fit their perception of the tone(s), they had just heard (Deutsch, 1981).
The set-up for the testing was quite simple. JVC Gumy Ear Bud Headphones, HA-F150A stereo speaker headphones, with a frequency response of 16-20,000 Hz (JVC, 2010), was plugged into a MacBook Pro. The tone sequence was accessed and played back for the participant from an online source (Philomel Records). The tone consisted of an alternating pattern of 400 (G4) and 800 (G5) Hz (Deutsch, 1974). The clip was 30 seconds in length.
Screen Shot of the embedded music that the participants listened to.
At the conclusion of the clip, each participant was asked to pick one of the following options that best described their individual percept: (A) A high tone on the right alternating with a low tone on the left; (B) A high tone on the left alternating with a low tone on the right; (C) A tone switching from ear to ear with no change in pitch; (D) None of the above (explain) (Deutsch, 1981).
All data and statistics were processed by PASW, Predictive Analytics SoftWare, SPSS, Statistical Package for the Social Sciences, 18.0.
Results and Discussion
Of the 51 students who participated, 32 responded (A) a high tone on the right alternating with a low tone on the left (62.7%); 17 responded (B) a high tone on the left alternating with a low tone on the right (33.3%); 2 responded (C) a tone switching ear to ear with no change in pitch (3.9%). The data was then stratified for various variables. The first of the stratifications was handedness. The following is based from if the participant was right-handed. Of the students who were right-handed, it was found that 18 participants had musical training (56.3 %), while 14 did not (43.8%). Out of the right-handed participants (N=32), 30 participants responded with (A) a high tone on the right alternating with a low tone on the left (93.8%) and 2 participants responded with (B) a high tone on the left alternating with a low tone on the right (6.3%). The following is based from if the participant was left-handed. Of the students who were left-handed, it was found that 7 students had musical training (43.8%), while 9 did not (56.3%). Out of the left-handed participants (N=16), 0 students responded with (A) (0%), 15 students responded with (B) (93.8%) and 1 participant responded with (C) (6.3%). In general, this follows very well with the established trend; right-handed people hear the high tone on the right, while left-handed people are a bit more varied, but generally hear the high tone on the left.
The musical trend of this data set does not follow the pre-conceived notion that left-handed people are more likely to have musical training. Traditionally, the right hemisphere is viewed as the musical hemisphere, thus with the contralateral nature of the brain, left-handed people would stimulate the right hemisphere of the brain more often than right-handed people invoking musical tendencies. (Tramo, 2001). Further stratification of the data was performed to assess the trend in the data. It was found from the data set that if the participant was musical, he or she was more likely to be right-handed. But, due to the greater abundance of right-handed versus left-handed people in the study, it was also found that if a person was non-musical, he or she was more likely to be right-handed. For the complete statistical breakdown regarding handedness and musical training refer to Appendix A, Table 2 and Table 3.
The last set of data stratifications were performed with respect to each tone choice (A-C) perceived. 32 participants responded with having heard a high tone on the right, alternating with a low tone on the left, option A. Of these students, 20 students indicated having musical training (62.5%), while 12 did not (37.5%). Additionally, 30 of the 32 students who perceived the tone sequence associated with choice A were right-handed (93.8%) and 2 students were both-handed (6.3%). 17 students responded with having heard a high tone on the left, alternating with a low tone on the left, option B. Of these students, 6 indicated having musical training (35.3%), while the majority of this subset indicated not having musical training (N=11, 64.7%). Furthermore, 15 of the 17 students were left-handed (88.2%) and 2 were right-handed (11.8%). Lastly were those who perceived a tone switching from ear to ear with no change in pitch (C). Option (C) represented a very small portion of the data (N=2). Of these 2 students, both indicated having musical training, although one was left-handed and one was right-handed.
Conclusions and Recommendations
In general the results of the subjects from this experiment correlated well with those of previously published results. The majority of right-handed subjects responded by perceiving a high tone on the right alternating with a low tone on the left, while the results of the left-handed indicated that the majority of the left-handed subjects perceived a high tone on the left alternating with a low tone on the right. The most substantial difference between these results and previously published studies include the lack of variation within the left-handed participants. According to published findings, the perception of left-handed people should be more varied. The lack of variance in this current study can be attributed to a small sample size.
Additionally, the demographic statistics proved interesting. According to the data, musical training does not affect the tone that is perceived. Again, this could be attributed either to a lack of a relationship or a small sample size. To efficiently test this, a larger sample size is needed of both musically and non-musically trained participants that are equally divided with left- and right- handed subjects.
Overall, this research should be completed with more subjects that equally represent the left- and right-handed population. This would improve the sample and should, in theory, provide data that is more representative of the population.
References
Andorn, A.C., Vittorio, J.A., Bellflower, J.. “3H-spiroperidol binding in human temporal cortex (Brodmann areas 41-42) occurs at multiple high affinity states with serotonergic selectivity,” Psychopharmacology (Berl.), (1989:90), 4, 520-525.
Chambers, C. D., Mattingley, J. B., & Moss, S. A. “The octave illusion revisited: Suppression or fusion between ears?,” Journal of Experimental Psychology: Human Perception and Performance, (2002) 28(6), 1288-1302.
Deutsch, D. “An auditory illusion,” Nature (1974) 251, 307–309.
Deutsch, D. "An auditory illusion". Journal of the Acoustical Society of America (1974) 55, s18-s19.
Deutsch, D. “The Octave Illusion and Auditory Perceptual Integration,” Hearing Research and Theory, Volume 1 (1981), 1, 99-142, New York: Academic Press.
Deutsch, D. “The octave illusion in relation to handedness and familial handedness background,” Neuropsychologia (1983) 21 (3), 289–293
Deutsch, D. “Musical Illusions,” Encyclopedia of Neuroscience, (2009), 5, 1159-1167, Academic Press, Oxford.
JVC. 2010. HA-F150A Specifications. http://av.jvc.com/product.jsp?modelId=MODL028884&pathId=162&page=3
Philomel Records. Diana Deutsch’s Auditory Illusions. http://philomel.com/musical_illusions/example_octave_illusion.php
Tramo, M. J. “Music of the hemispheres,” Science. (2001), 5.
Varney, N. R. and Benton, A. L. “Tactile perception of direction in relation to handedness and familial handedness,” Neuropsychologia (1975), 13, 449-454.
Appendix A
Table 1
| Age | |||||
| | Frequency | Percent | Valid Percent | Cumulative Percent | |
| Valid | 17 | 6 | 11.8 | 11.8 | 11.8 |
| 18 | 14 | 27.5 | 27.5 | 39.2 | |
| 19 | 11 | 21.6 | 21.6 | 60.8 | |
| 20 | 12 | 23.5 | 23.5 | 84.3 | |
| 21 | 6 | 11.8 | 11.8 | 96.1 | |
| 22 | 2 | 3.9 | 3.9 | 100.0 | |
| Total | 51 | 100.0 | 100.0 | | |
Ages of the participants
Table 2
| Musical | |||||
| | Frequency | Percent | Valid Percent | Cumulative Percent | |
| Valid | Y | 18 | 56.3 | 56.3 | 56.3 |
| N | 14 | 43.8 | 43.8 | 100.0 | |
| Total | 32 | 100.0 | 100.0 | | |
Whether the participant had musical training (Y=Yes, N=No) with respect to the right-handed participants.
Table 3
| Musical | |||||
| | Frequency | Percent | Valid Percent | Cumulative Percent | |
| Valid | Y | 7 | 43.8 | 43.8 | 43.8 |
| N | 9 | 56.3 | 56.3 | 100.0 | |
| Total | 16 | 100.0 | 100.0 | | |
Whether the participant had musical training (Y=Yes, N=No) with respect to the left-handed participants.
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