Summary of Thorndike's Law of Effect: Empirical Study

## Introduction This study material summarizes a psychology experiment in which participants were trained to draw lines of specific lengths while blindfolded. The study investigates how feedback labeled "right" or "wrong" influences performance compared with mere repetition without feedback. The goal is to help a not-attending student understand the methods, results, and practical implications of such perceptual-motor training experiments. ## Experiment overview ### Purpose - To examine whether simple verbal feedback ("right" / "wrong") given after a response alters future performance when participants draw lines with eyes closed. - To compare the effects of feedback against mere repetition without feedback. ### Basic procedure (general format) 1. Participants (S) sat blindfolded at a table with a drawing board and a fixed starting edge (a strip of veneer) on the left. 2. A sheet of cross-section paper was fixed so that the experimenter could measure line lengths from the veneer as zero. 3. The participant was instructed to draw, in one continuous quick movement, a line of a specified length (3 in., 4 in., 5 in., or 6 in.), always starting at the left edge. 4. After each drawn line, the participant waited until the experimenter announced the response quality before drawing the next line. ### Feedback definitions > **Definition:** In the training condition, the experimenter said "right" when the drawn line fell within a specified tolerance of the target length and "wrong" otherwise. For 3-inch lines the tolerance was $\tfrac{1}{8}$ in.; for 4-, 5-, and 6-inch lines the tolerance was $\tfrac{1}{4}$ in. ### Training schedule and measurement - Participants drew many trials across several sessions. Typical schedules included multiple training periods (e.g., seven training periods) with short rests between trials. - Two tests were given: an early test before training and a late test after training. No feedback was given during tests. - Percent of "right" responses and average absolute deviations from target lengths were computed to quantify improvement. ## Key elements of experimental design ### Controlled starting point - A fixed veneer strip gave a consistent zero point for all lines, reducing variability due to starting position. ### One continuous movement - Each line was drawn in a single, quick stroke to keep the motor pattern consistent across trials. ### Immediate verbal feedback - The only consequence used was a short verbal evaluation given about 2 seconds after the participant announced the response. No information about magnitude or direction of error was provided. ### Comparison condition (no-feedback control) - A smaller control sample drew the same number of lines but received no verbal feedback. This tests whether improvement results from feedback specifically or from mere repetition. ## Results summary (what was observed) - Participants receiving feedback showed clear improvement: percent of "right" responses increased substantially during training and stayed higher in the late test than in the early test. - Average errors (absolute deviations) decreased for most participants after feedback training. - Participants in the no-feedback control condition showed smaller and inconsistent reductions in error, suggesting that feedback produced much of the improvement. ## Representative quantitative ideas - Training raised median percent-correct from roughly 13% in early tests to about 54% during later training periods, with a late-test median around 26% — higher than the early-test baseline. - Across participants and line lengths, the average reduction in absolute error after feedback training was statistically meaningful in the study (reported as several times its probable error). ## Tables: Comparing feedback vs. repetition | Feature | Feedback training ("right"/"wrong") | Mere repetition (no feedback) | |---|---:|---:| | Verbal consequence | Yes: "right" or "wrong" after each trial | No verbal