Navigating an ambiguous world

In our daily lives, we are constantly surrounded by or exposed to various sounds, images or speech, many of which feature ambiguity. From our previous experiences with objects our brain interprets it without even consciously thinking about it. Similarly, the sound is a product of our environment and one task of our auditory system is to take the overlapping waves arriving from various sources at our ears as a single mixture and decode, either by integrating or segregating the musical harmony as a model for perception.

As Kris Ernst (1952, p. 259) describes, ambiguity frequently leads to an aesthetic response. Such a response shapes the re-creation of objects at shifting psychic levels or distances.  

Dr. Alex Billig re-introduces the concept of auditory ambiguity as an interest of scientific inquiry. In his view, it’s potentially valuable to use the music as a proponent enabling to examine what really is happening at a level of controlled perception when studying mind and brain.

In Billig et al.’s study (2018), he focused on understanding the shifting psychic levels and what affects how we perceive two different sounds. He did this by looking at the neural activity when exposed to a stimulus from the same source. Once the model of neural signatures is obtained, we can ask to what extent can people influence how they perceive what they hear. Billig was able to demonstrate with the subjective and objective measures that participants were indeed able to exert a significant level of control over hearing integration or segregation of tones.

Researching how intention and experience can act on and shape auditory perception

During his talk, Billig elaborates on the knowledge gained from researching what happens when people manipulate their auditory perception. He mentions the ability of a musical conductor to hone in on different aspects of their orchestra as an example of how people report being able to change their perception at will in order to listen to what they want to hear.

He brings up his experimental research (Billig et al., 2018), where he recruited 23 participants to report on their own perceptions whilst listening to a musical sequence with two tonal streams. He separated them into three listening conditions; a neutral condition, a condition where they were asked to attempt integrated listening and a condition where they were asked to attempt segregated listening. He concluded that people can influence their auditory perception. In addition, in the last condition, adjusting the sequence to low and high tones, he found that increasing the frequency separation makes participants more able to hear the two streams separately.

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Figure 1. A graph demonstrating the percentage of the time participants reported auditory segregation in the three conditions and tone frequencies from Billig et al.’s (2018) study.

However, Billig also mentioned that there could be a bias in the reporting of these perceptions. Participants could report that they perceive different tones when they don’t, in order to please the researcher, or they could give themselves credit for perception changes that would have occurred anyway (for example, looking at an optical illusion for an extended period of time, making someone susceptible to seeing the alternatives).

This is why Billig highlights the importance of research into the neural activity involved. He asks whether people can put themselves in a state where they can manipulate the neural activity that is reflecting the sounds they’re hearing and, in doing so, change their perception of those sounds.

Support for subjective claims

Billig et al.’s 2018 study relied on incorporating objective measures like magnetoencephalography (MEG) neuroimaging techniques with the subjective participant reports. One aspect of the MEG data allowed them to map the activity to locations in bilateral posteromedial Heschl’s gyrus. He further showed that this neural activity phase-locks with the stimuli in the very early stages of processing. These neural correlates provide strong support for many of the subjective claims examined. By supplementing subjective measures with a variety of objective measures, a deeper understanding of auditory ambiguity can be obtained.

Subjective measures can also be combined with other objective behavioural measures to create a mixed methods design. In an experiment about lexical streaming, Billig and colleagues (2013) asked participants to listen to an audio stream and press a button to report if a stream of sounds sounded like one word or two separate sounds. They also included a button pressing task asking participants to identify a gap in sound; the objective measure in this experiment. Interestingly, they found that both the objective and the subjective measures of detecting that gap support the same conclusion. When nonwords are presented, participants segregate more readily but this is more difficult when presented with word stimuli. Subsequently, gap detection in the sounds is better when the participant hears the sound as one, integrated unit rather than as separate sounds. Here mixed methods were very effective in exploring effects such as language on low-level perception.

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Figure 2. Mixed methods approach to investigating lexical streaming from Billig et al. (2013).

Figure A illustrates how the subjective button presses are integrated with the objective deviation in stimuli, serving as the experimental target over time. The deviation occurs in the audio track in several places but as illustrated, listeners detect the difference more readily when they are streaming. Figure B shows the participant set-up for the completion of this task.

What does auditory ambiguity tell us about the mind and brain?

Billig’s talk highlighted the importance of conducting research into auditory ambiguity, given how frequently it occurs in our daily lives. Although occurrences of auditory ambiguity may seem trivial, these events are partly responsible for shaping our perceptions, as indicated by both self-reports and neural activity observations.  

On the surface, auditory ambiguity may seem like a straightforward idea, but dig deeper and you’ll find it’s laced with all sorts of weird and wonderful mechanisms researchers like Billig have only just started to explore.

It should have been difficult to understand such an inherently vague concept, however Billig’s use of well-known examples, such as the Laurel-Yanny phenomenon, helped to illustrate just how ubiquitous auditory ambiguity is in our lives.

While his lecture raised questions as to whether one is in control of auditory ambiguity, Billig acknowledged that our understanding is still in its infancy and that there is still much to be learned about the constraints of ambiguity. He concluded that music provides the ideal stimuli for such research, which is good news for budding music psychologists among you interested in pursuing this line of enquiry!

Time limitations and technology glitches aside, Billig presented a talk that was highly informative and delivered in such a way that made this mind-boggling topic more understandable. Moreover, many found it inspiring to hear from a former MMB student about his career trajectory and current work.

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Figure 3. Just how much do you control your auditory perception? Image: Jake Fried via thisiscolossal.com

By Marcela Palejova, Melena John, Patrick Smith and Isa Jaward.

 

References

Billig, A. J., Davis, M. H., & Carlyon, R. P. (2018). Neural decoding of bistable sounds reveals an effect of intention on perceptual organization. Journal of Neuroscience (38), 3022-17.

Billig, A. J., Davis, M.H., Deeks, J.M., Jolijn, M., & Carlyon, R.P. (2013). Lexical influences on auditory streaming. Current Biology (23), 1585-1589.

Gutschalk, A., & Dykstra, A.R. (2014). Functional imaging of auditory scene analysis. Hearing Research (307), 98-110.

Kris, E. (1952). Psychoanalytic explorations in art. New York: International Universities Press, Inc.

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