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Manchester Based Audio Studio. Sound Design | Voice Over/ADR | Foley | 5.1 Mixing | Pro Tools | Education | Sound Effects Libraries

ARTICLE: Auditory Illusions Exposed: Why You Can't Trust Your Ears!

The Brainstorm/Green Needle Auditory Illusion

In the digital age, the internet continues to be a breeding ground for intriguing and often mind-boggling phenomena. A classic example that captivated online communities in 2019 is the "Brainstorm/Green Needle" auditory illusion. This peculiar occurrence involves a short video clip featuring a plastic toy emitting a sound. However, what makes this phenomenon truly baffling is that individuals claim to hear distinct phrases depending on which word they consciously focus on: "brainstorm" or "green needle”. The illusion offers a glimpse into the intricacies of how we perceive audio. Check out the phenomenon here:

Central to this illusion is the concept of expectation. When we’re primed with a specific word or visual cue, our brains seem to interpret the sounds to match that expectation. The Brainstorm/Green Needle illusion highlights the influence of suggestion on how we perceive sound. The mere act of consciously directing one's attention towards a specific word or visual cue can alter the way we interpret audio.

The Shepards tone & Risset Rhythm

The Shepard's Tone, named after cognitive scientist Roger Shepard, is a phenomenon that creates the illusion of an endlessly ascending pitch, despite the absence of any actual increase in frequency. Picture yourself adjusting the tension of a stringed instrument, gradually increasing the pitch with each turn. As the tension rises, you anticipate the string reaching its breaking point but despite the escalating tension, the pitch remains unchanged.

This illusion is achieved by layering multiple tones at different octaves, fading in and out in a carefully choreographed manner. As one layer fades out, another fades in at a higher octave, creating a seamless transition that gives the impression of continuous ascent. Hans Zimmer skilfully demonstrates the use of the Shepard's Tone throughout his work, being featured in movies such as Batman and Dunkirk.

While the Shepard tone primarily focuses on pitch perception, the Risset rhythm, on the other hand, applies this illusionary effect to the domain of rhythm.

The Risset rhythm is achieved by layering multiple rhythms, each playing at a faster tempo than the one preceding it. As one rhythm accelerates, another slower rhythm fades in, creating a seamless transition that gives the impression of a never-ending increase or decrease in tempo.

The Tritone Paradox

The Tritone Paradox is another intriguing auditory illusion that plays with our perception of pitch. It involves presenting listeners with pairs of tones, with one ascending and the other descending, yet some individuals perceive the direction of the pitch differently. For instance, one person might interpret the sequence as ascending, while another might perceive it as descending. This paradox sheds light on the intricate relationship between how we perceive audio and the cognitive mechanisms responsible for interpreting musical intervals. It sheds light on the subjectivity and complexity that underlie our experience of sound.

The Continuity Illusion

The Continuity Illusion challenges our conventional understanding of sound perception by demonstrating the brain's ability to bridge gaps in auditory input, creating an uninterrupted flow of sound. The Continuity Illusion is a phenomenon in which a continuous sound appears to persist even when briefly interrupted by a moment of silence. In other words, the brain "fills in" the gap in the audio, creating the illusion of uninterrupted sound.

Understanding the Continuity Illusion requires delving into the intricate workings of the auditory system. When a sound signal reaches our ears, it undergoes a series of processes in the auditory cortex of the brain. The brain interprets the frequency, intensity, and duration of the sound, creating a perceptual representation. When a momentary interruption occurs, the brain employs predictive processing, a mechanism that uses prior knowledge and context to "fill in" the missing information. This predictive processing allows us to maintain a seamless stream of sound, even in the face of interruptions.

Binaural Beats

Binaural beats is a phenomenon that occurs when two slightly different frequencies are presented separately to each ear. The brain perceives a third frequency, which is the mathematical difference between the two presented frequencies. This perceived beat is not an actual sound, but rather an auditory illusion created by the brain's processing of the different frequencies.

For example, if one ear hears a tone at 300 Hz and the other ear hears a tone at 310 Hz, the brain perceives a third tone at 10 Hz. This is called a binaural beat. This beat is often described as a pulsing or throbbing sensation.

Binaural beats have been studied for their potential effects on cognitive processes, relaxation, and meditation. Some people use binaural beats as a tool for achieving altered states of consciousness or for enhancing focus and relaxation.


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