Stimulus generalization, discrimination learning, and peak shift in horses.
Abstract: Using horses, we investigated three aspects of the stimulus control of lever-pressing behavior: stimulus generalization, discrimination learning, and peak shift. Nine solid black circles, ranging in size from 0.5 in. to 4.5 in. (1.3 cm to 11.4 cm) served as stimuli. Each horse was shaped, using successive approximations, to press a rat lever with its lip in the presence of a positive stimulus, the 2.5-in. (6.4-cm) circle. Shaping proceeded quickly and was comparable to that of other laboratory organisms. After responding was maintained on a variable-interval 30-s schedule, stimulus generalization gradients were collected from 2 horses prior to discrimination training. During discrimination training, grain followed lever presses in the presence of a positive stimulus (a 2.5-in circle) and never followed lever presses in the presence of a negative stimulus (a 1.5-in. [3.8-cm] circle). Three horses met a criterion of zero responses to the negative stimulus in fewer than 15 sessions. Horses given stimulus generalization testing prior to discrimination training produced symmetrical gradients; horses given discrimination training prior to generalization testing produced asymmetrical gradients. The peak of these gradients shifted away from the negative stimulus. These results are consistent with discrimination, stimulus generalization, and peak-shift phenomena observed in other organisms.
Publication Date: 1991-07-01 PubMed ID: 1940765PubMed Central: PMC1323085DOI: 10.1901/jeab.1991.56-97Google Scholar: Lookup
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- Journal Article
Summary
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The research investigates how horses are able to learn from stimuli, showing their ability to generalize from stimuli, learn how to discriminate between different stimuli, and adapt their response accordingly (known as peak shift). The experiments used circles of different sizes as the stimuli and taught the horses to press a lever in the presence of a certain sized circle.
Stimulus Generalization
- The study began by exploring stimulus generalization, which is the tendency of a subject to respond to stimuli that are similar but not identical to the original stimulus.
- The researchers used a range of circles from 0.5-inch to 4.5-inch as stimuli and trained the horses to press a lever when they saw a 2.5-inch circle – this was the ‘positive’ stimulus. Two horses out of the sample set were tested on their stimulus generalization before they were trained on discrimination.
- The intention was to understand if the horses could transfer the response from the 2.5-inch circle to other similar circles.
Discrimination Learning
- Following the test on stimulus generalization, the horses were then trained on discrimination learning, which involves learning to distinguish the positive stimulus from a negative one and responding accordingly.
- In this phase, the positive stimulus which prompts the horse to press the lever was the 2.5-inch circle and the negative stimulus which should not prompt a lever press was the 1.5-inch circle.
- Three horses met a criterion of zero responses to the negative stimulus in fewer than 15 sessions. This showed that the horses were able to quickly learn and differentiate between the positive and negative stimulus.
Peak Shift
- The last part of the experiment looked at the concept of “peak shift”. This is a behavior change in which the peak response is shifted away from the original stimulus towards a more exaggerated stimulus.
- For the horses that were given discrimination training before generalization testing, their peak response shifted away from the negative stimulus.
- This indicates that they adjusted their behaviour based on prior training, showing a more exaggerated response to similar but not negative stimuli.
Overall Findings
- Overall, the results of this study align with previous research on discrimination, stimulus generalization, and peak-shift phenomena observed in other organisms.
- It showed that horses, like other laboratory animals, can exhibit stimulus control behaviours, giving valuable insights into the cognitive processes of these animals.
Cite This Article
APA
Dougherty DM, Lewis P.
(1991).
Stimulus generalization, discrimination learning, and peak shift in horses.
J Exp Anal Behav, 56(1), 97-104.
https://doi.org/10.1901/jeab.1991.56-97 Publication
Researcher Affiliations
- Department of Psychology, Ohio University, Athens 45701.
MeSH Terms
- Animals
- Appetitive Behavior
- Attention
- Conditioning, Operant
- Discrimination Learning
- Female
- Generalization, Stimulus
- Horses / psychology
- Male
- Pattern Recognition, Visual
- Size Perception
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Citations
This article has been cited 9 times.- Kappel S, Ramirez Montes De Oca MA, Collins S, Herborn K, Mendl M, Fureix C. Do you see what I see? Testing horses' ability to recognise real-life objects from 2D computer projections. Anim Cogn 2023 Jul;26(4):1147-1159.
- Ragonese G, Baragli P, Mariti C, Gazzano A, Lanatà A, Ferlazzo A, Fazio E, Cravana C. Interspecific two-dimensional visual discrimination of faces in horses (Equus caballus). PLoS One 2021;16(2):e0247310.
- Lin IR, Chiao CC. Visual Equivalence and Amodal Completion in Cuttlefish. Front Physiol 2017;8:40.
- Derenne A. Shifts in postdiscrimination gradients within a stimulus dimension based on bilateral facial symmetry. J Exp Anal Behav 2010 May;93(3):485-94.
- Wisniewski MG, Church BA, Mercado E 3rd. Learning-related shifts in generalization gradients for complex sounds. Learn Behav 2009 Nov;37(4):325-35.
- Miyashita Y, Nakajima S, Imada H. Differential outcome effect in the horse. J Exp Anal Behav 2000 Sep;74(2):245-53.
- Dougherty DM, Lewis P. Generalization of a tactile stimulus in horses. J Exp Anal Behav 1993 May;59(3):521-8.
- Ricci-Bonot C, Brosche K, Baragli P, Nicol C. A systematic review on the effect of individual characteristics and management practices on equine cognition. Anim Cogn 2025 Nov 26;28(1):96.
- Caldicott L, Pike TW, Zulch HE, Mills DS, Williams FJ, Elliker KR, Hutchings B, Wilkinson A. Odour generalisation and detection dog training. Anim Cogn 2024 Nov 1;27(1):73.
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