The Making of Microdreams

Part 2. Sensory Incorporation in Microdreams.

My previous blog introduced the study of microdreams--those fleeting images that occur as you fall asleep-- and covered some examples of how real sensory stimuli can be incorporated into microdreams. For example, if you fall asleep in class, the sensation of your head literally nodding off might create the visual 'microdream' image of a book falling over.

A key question to ask is, how exactly do sensory stimuli get transformed into images, seemingly in real time?

Tore Nielsen, author of the recent paper ‘Microdream neurophenomenology’ deconstructs this process using examples of his own microdreams that were directly influenced by external stimuli, such as sudden sounds, lights, or body movements, which were then incorporated into imagery (what he terms ‘exosensory imagery’).

Nielsen noticed that often an external stimulus appears as a rather abrupt movement in imagery, in his words, “movement that seems to have been caught in mid-expression…a vigorous, even violent, movement in a downward or circular direction.”

He gives some anecdotal examples where fleeting images that appeared while dozing off were suddenly transformed by real-world stimuli. In one microdream, the ‘whop’ of a tennis ball hitting the ground causes an image of an arm to be suddenly slapped by a hand; in another example, the clatter of an Ikea cash register causes an image of a clown to suddenly spring into a somersault. In two further examples, a sudden dip in airplane turbulence caused, first, an image of a girl to suddenly fall to her knees, and second, an image of a woman to suddenly spill a glass of wine.

In many of these examples, the modality of the stimulus matches the imagery in a “direct” incorporation, e.g. auditory stimuli affect sound imagery (the ‘whop’ of a tennis ball becomes the ‘slap’ of an arm) and vestibular stimuli affect balance (a dipping airplane becomes ‘falling’ imagery). However, in other examples, the sensory modality is transformed; in the clown dream, for instance, a clattering sound led to visual movement in imagery. This is an example of an indirect, “projected” incorporation.

Studies of nighttime dreams have also shown that real sensory stimulation can be incorporated in both direct or projected ways into dreams. For example, a participant sleeping in the laboratory with a pressure cuff wrapped around their leg might dream of a cat brushing up against their leg (direct incorporation) or of a horse hurting its ankle (projected incorporation). (See previous post on Sensory Incorporation in Dreams for more detail.)

As Nielsen demonstrates, this process of sensory incorporation is more easily observed in microdreams.

In fact, through a series of microdreams, Nielsen found that an auditory stimulus enacting a visual change in imagery is the most common form of ‘projected’ incorporation. In one example, while at a conference and dozing off (like any good scientist), he has the following experience:

“[Image:] A heavy door made of wood suddenly swings open to the R and slams against the corner of a counter top. [Reality:] The conference speaker made a thudding sound by hitting the microphone. The sound corresponded exactly with the door slam in the image. A slide on the screen just pre-image depicted a closed, large, brown wooden door.”

In this case, as the speaker hits the microphone with a thud, Nielsen simultaneously imagines a door swinging open and hitting a counter. Let’s examine this more closely. The sound of the microphone caused the 'door-slamming' image to occur, but somehow, the initial swinging open of the door seems to have occurred prior to the microphone sound.

This is the logical conundrum of incorporation:

“that an external stimulus so quickly elicits a set of image features, some of which seem to temporally precede the stimulus. […] the sound of a tennis racquet striking a ball is not only incorporated directly as a hand slap sound, but visual details preceding the slap are also represented, i.e. the hand falling prior to it slapping. […] the sound of a microphone being bumped is incorporated directly into the image as the sound of a door slamming, yet it also elicits the visual image of a swinging door that seems to precede the sound. The stimuli in both cases presumably elicit visual details that are appropriate to, and thus help contextualize, the sound stimuli, but that also seem to occur just before the sounds themselves.”

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So how is this possible? How did the image of a swinging door appear prior to the sound of the microphone thud?

Well, in fact, even in waking life, our mind can shift and alter our perception of stimuli in order to better match expectations, to better ‘make sense’ of experience. For example, in audiovisual experiments, if you see an image of two blocks on a screen hitting each other, and you hear a sound slightly before this visual collision, your mind will actually delay perception of the sound in order to match the visual timing of the blocks hitting. In a more common experience, if the video on a TV program is slightly delayed behind the audio, you will still perceive the speech as occurring in sync with the actors’ speaking.

In other examples, our mind may shift the location of a sound in order to match a visual event. “The visual event is said to ‘capture’ the sound’s location as in the ‘ventriloquist effect’ (Howard and Templeton, 1966) in which a visual stimulus (the dummy’s mouth) captures the verbal stimulus (the ventriloquist’s voice) forcing a multisensory illusion of integration.”

According to this view of ‘multisensory integration’, then, the stimulus sounds in the microdream examples (tennis ‘whop’ and microphone ‘thud’) may immediately evoke associated visual images, but perception of the sound is essentially paused in order for the generated image to ‘capture’ the sound. The visual images then seem to occur before the very sounds that triggered them.

All of these microdream examples point to the incredible improvisation of imagery even when disrupted by sudden sensory input, the mind’s capacity for sensemaking in a world of undpredictability, whether we are awake or dreaming.