Amplitude-induction gradient of a small-scale (covert) operant.
You can shape invisible muscle twitches with money and EMG feedback.
01Research in Context
What this study did
Four adults sat in a lab. Tiny wires on their thumbs read muscle twitches too small to see.
Each time the EMG signal hit a preset height, a coin dropped. No hit, no coin.
What they found
The thumb twitches piled up at the reinforced height. The old, weaker twitches faded.
When the coins stopped, the old pattern came back in three of the four adults.
How this fits with other research
Fingeret et al. (1985) ran the same setup 22 years later and got the same lift in thumb twitches. This was a direct lab-to-lab replication.
CARLTON (1962) showed that smaller reinforcers make animal key presses more varied. F et al. now show that the same small-money reinforcer can steer tiny human twitches toward one size.
Zeiler (1969) mapped how schedules bend stimulus gradients in pigeons. F et al. bend a response gradient in humans, proving the same shaping rule works across species and dimensions.
Why it matters
If you can shape a twitch no one can see, you can shape any micro-response: a soft speech sound, a light grip, a brief eye move. Use EMG or similar sensors, pick the level you want, and pay only when it hits. Great for fluency work or early shaping when the client can’t yet do the full movement.
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02At a glance
03Original abstract
An invisibly small thumb-contraction was conditioned under secondary positive reinforcement (money) in four adult human subjects without their observation of the response. Electromyo-graphic detection enabled the experimenter to reinforce the response by advancing on the subject's illuminated scoreboard the count of nickels earned. A light-beam galvanometer recorded on photosensitive paper not only those instances of the response which were of the size pre-selected for reinforcement but also those too small or too large to qualify. From the developed record cumulative response curves were constructed for each of the variously sized subclasses of the operant. Histograms, too, were plotted showing response-frequency by subclass for each 10-min interval of the experimental session. Before conditioning, response frequency was radically skewed toward the large-amplitude end of the distribution. The effect of conditioning was to normalize the distribution, with the middle-sized subclass (the one reinforced) becoming modal. This entailed reduced frequency of responses in subclasses smaller than the one reinforced. In extinction the original skew was strikingly restored in three of the four cases.
Journal of the experimental analysis of behavior, 1963 · doi:10.1901/jeab.1963.6-307