Spatial Peak Shift and Generalisation in Humans

General Methods

In these experiments, Marcia Spetch and I presented university students with a computer betting game. On any one trial, one location was marked by a blue square on a computer monitor (not five, as in the figure). Students were invited to bet 0 to 4 points. A winning location (S+, there was only one for each student) won them four times the points betted. Other locations shown during training (zero to four across experiments), were losing locations (S-s).

After sufficient training, they were occasionally tested in various ways. They were asked to bet on a range of locations, including those used during training. They were shown a location on the monitor and asked if it was the one that won them the most points. And, without anything shown on the screen, they were asked to point to S+ (the most winning location).


Generalisation Results

 

We obtained generalisation gradients on betting after training without any S-s.

These were exponential in shape, supporting Shepard's law. See related story on spatial generalisation in bees.


Betting Results

 

When betting after peak shift training (some S-s),

subjects betted more on the S+ side than on the S- side, a pattern that is called area shift.


Results on Verbal Questions

 

When asked whether a location was the most winning one,

subjects under some conditions showed a systematic error (peak shift): they were more likely to name another location than S+ as the most winning one. This happened when they had sufficient betting experience on the S- side but not on the S+ side.


Pointing Results

 

When asked to point to the most winning location, subjects made systematic errors.

In this figure, subjects with vertical training acted as a control group. Their S-s were vertically displaced from S+. The horizontal group had S-s horizontally displaced from S+. While both groups showed some systematic errors in the horizontal direction, the horizontal group showed significantly more. This indicates peak shift induced by the training.


In summary,

Humans thus show peak shift or area shift in the spatial domain in three different ways.

 

Reference

Cheng, K., & Spetch, M.L. (2002). Spatial generalization and peak shift in humans. Learning and Motivation, 33, 358-389.


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