The Octave Illusion

Posted by Thomas Scarborough*

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440Hz and 880Hz alternating R and L

The Octave Illusion was discovered by Diana Deutsch in 1973. It produced two alternating tones, one octave apart, in each ear. However, when the tone in one ear went ‘high’, the tone in the other ear went ‘low’, and vice versa. (Click the arrow to play.)

The tones used here are A4 (440 Hz) and A5 (880 Hz) - in this case reproduced with the precision of the modern computer. The effect is the same whether this is played through headphones or loudspeakers -- and interestingly, does not change when the headphones or loudspeakers are swapped around.

It is a simple auditory illusion, yet most powerful. Instead of hearing two alternating tones in each ear - as one should - most people hear alternating tones bouncing from ear to ear. It seems that the brain has therefore removed two tones, one from each ear. That is, the tones are replaced with silences.

There is copious literature on what this might mean, and what might cause the effect - yet the general agreement is that there is no simple explanation.

It might not seem at first that an auditory illusion has anything to do with philosophy. However, what we have in this particular case is auditory ‘objects’ -- a range of auditory ‘things’ which include bangs, ringtones, meows, and so on -- which belong to the much larger set of ‘objects’ in general.

To this day, then, we search for ways to decide what is or is not illusory ...

space, time, numbers

identity, free will

things, events, properties

society, language

money

matter, force, energy

causes, physical laws...

... and even God.

Thus, illusions such as that above -- of which we all now are aware -- have a lot to do with the way we perceive our world.  It has not always been so. There once was a time - or so it is thought - where we perceived everything as real. Today, to borrow the words of the British philosophy professor Simon Blackburn, we have left this far behind: ‘Everything you can think of has at some time or another been declared to be a fiction by philosophers.’

It falls under the subject of ontology - and it all started, according to the eighteenth century Scottish philosopher, Thomas Reid, when we separated objects from ideas. The Octave Illusion is just one of many evidences that our experience is not the same as the ideas we have about it. Our brains have already interpreted it for us.

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* The author once designed a simple electronic unit to produce this effect. This is still obtainable from the publisher at https://www.elektormagazine.com/magazine/elektor-200411/17842

Picture Post # 24 The Privilege of Being Near and Far

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'Because things don’t appear to be the known thing; they aren’t what they seemed to be neither will they become what they might appear to become.'

Posted by Tessa den Uyl and Martin Cohen

Image credit: from an original photographic plate created by Thomas Scarborough

The pictured child is not far, but too far to be near; or too close to be far, but not that near.  Instead, they are halfway, as the background, or foreground" seem to be as well. In-between is where we make distinctions; the difference is always in-between. But rather than representing elements between which a difference is made, this picture seems to represent the in-between itself.

Humidity and temperature change have touched the chemicals of this slide, and ‘X-rayed by life’ in this way, existence reaffirms itself as an ever-changing movement. Within the invisible that becomes visible, we might think to collect memories, freeze moments into pictures, and hence even to think of something as permanent...  yet, little by little, these perceptions are all erased by the visible that withdraws into the unknown.

Stability does not exist. The in-between hands to us that what we think, but do not truly know, and maybe if life would see us, it would say ‘we do not know much’. Thoughts alone make a thread that by stiff perseverance does not break, however often we may have to observe that the tissue is of dubious nature...