Ear and pitch segregation in Deutsch’s octave illusion persist following switch from stimulus alternation to repetition

Abstract

Deutsch's octave illusion occurs when two tones that are spaced an octave apart are repeatedly presented in alternation; the sequence is presented to both ears simultaneously but offset by one tone, so that two dichotic chords are repeatedly presented in alternation. The most common illusory percept consists of an intermittent high tone in one ear alternating with an intermittent low tone in the other ear. The aim of this study was to investigate whether, once the illusory percept has emerged, the illusion will persist when the original sequence is followed by another sequence consisting of the repeated presentation of one of the two dichotic chords. Forty naïve subjects were tested with stimuli consisting first of a priming sequence containing dichotic octaves alternating between ears followed immediately by a test sequence consisting of a single dichotic octave presented repeatedly. The durations of the priming and test sequences were manipulated. The findings showed that the illusory percept is maintained after the switch from alternation to repetition and that the relative length of the priming and test sequences has a negligible influence on the persistence of the illusory percept.

Theta-burst stimulation causally affects side perception in the Deutsch’s octave illusion

“…Overall, our results confirm involvement of the left IPL in the perception of side (illusory ear of origin) during the Deutsch’s octave illusion as previously suggested by the MEG studies of evoked activity 7 , 8 . Associating brain activity with the subjective report during the illusion, Brancucci and colleagues 8 found the brain areas specifically processing the illusory percept. In particular, the pitch percept was specifically associated with activity in Heschl’s gyrus, the medial temporal and the superior frontal gyri, as well as in the right inferior frontal gyrus.…”

“…In particular, such alteration was present in the first run (i.e., first 10 minutes) after cTBS, which was delivered offline to the left IPL before the auditory stimulation. On the contrary, no alteration of the standard illusion (i.e., the last tone more often perceived at the right ear, as observed in the present preliminary experiment and in the referenced study 8 ) was noted after cTBS on left pIPS. Later, during the second run (i.e., second 10 minutes), the effect of the magnetic stimulation faded and the perception of the illusion was no longer influenced by the cTBS on left IPL, thus becoming similar in the two brain stimulation conditions.…”

“…In particular they were asked to press “Q”, with left index finger, when the last tone was perceived at the left ear, and to press “P”, with the right index finger, when the last tone was perceived at the right ear. To test whether this paradigm is consistent with previous observations 8 showing a right-ear preponderance (i.e., subjects more often perceived the last tone of the block at the right ear), we first enrolled a group of right-handed (Edinburgh Inventory Index 15 : 81 ± 13) subjects ( N = 15; 5 females), who were asked to perform a run of the main experiment without cTBS. As expected, one-way ANOVA confirmed the previous findings (F1,14 = 10.42, p = 0.006), indicating that the subjects perceived the last tone of the block more often on the right (53.6% ± 4.3) than on the left (46.4% ± 4.3) ear.…”

“…In the present study, we used repetitive transcranial magnetic stimulation (rTMS), specifically continuous theta-burst stimulation (cTBS), to inhibit the left IPL in order to test the possible causal role of this area in the deceived perception of side during the Deutsch’s octave illusion 8 . In addition, we inhibited the left inferior parietal sulcus (pIPS) as a control area.…”

Grouping Mechanisms in Music

“…An interesting study by Brancucci, Lugli, Santucci, and Tommasi (2011) showed that once the octave illusion is induced, its effect can persist strongly. The subjects were presented first with a priming sequence consisting of the octave illusion pattern, and then repeatedly with a test sequence consisting of one of the alternating dichotic chords (either 400 Hz right/800 Hz left, or 800 Hz right/400 Hz left) for up to 6 s. For all the test sequences, the repeating dichotic chords continued to be heard as in the illusion.…”