Cognitive bias in animals

1. Cognitive bias in animals

2. Do animals get depressed or anxious? If they do, how will we know? In both humans and animals, what is the function of these emotions?

3. First paper: Cognitive bias and affective state Emma J. Harding, Elizabeth S. Paul, Michael Mendl

4. Study procedure • Rats were trained to respond by pressing a lever when hearing one tone to get food, and to refrain from pressing the lever in response to another tone to avoid an unpleasant noise • Once trained, the rats were allocated to either “predictable” housing or to “unpredictable” housing Unpredictable housing involved between zero and two interventions at random times each day. Interventions included: • unfamiliar cage, or tilted cage • sharing cage with conspecific stranger • light/dark cycle temporarily reversed • bedding left damp

5. Trial procedure • After 9 days in the assigned housing, the rats were exposed to non-reinforced tones that had frequencies intermediate between those of the food-delivery and noise-avoidance tones • The two treatment groups, predictable housing vs. unpredictable housing, were compared for the willingness and speed with which the rats pressed the lever in response to these ambiguous tones

6. Figure caption Mean (±1 s.e.) responses to tones during 10 daily 30-min test sessions for male Lister hooded rats housed under 'predictable' (open circles, n = 4) and 'unpredictable' (filled circles, n = 5) conditions. a, Proportion of tones to which the animals responded to by pressing a lever. b, Latent time between sounding of the tone and pressing of the lever. 'Noise' and 'food' tones are the tones used during training (2 and 4 kHz, respectively, for about half of the rats, and 4 and 2 kHz, respectively, for the remaining rats). 'Probe' tones are non-reinforced, intermediate tones (2.5, 3, 3.5 kHz), each randomly interspersed with a probability of 0.085 between the reinforced training tones. Regression equations were calculated for each rat, correcting for nonlinear relationships by using binary logistic regression (for proportions) and logarithmic transformations for linear regression (for latencies). Animals were checked daily and remained healthy throughout the experiments.

7. Addresses what the authors claim is a potential confound in the Harding et al. paper by using a choice procedure. • Looks at the effect of enriched housing relative to standard animal care practices for starlings.

8. Choice task • A light is on for 2 or 10 seconds, after which the bird must choose between pecking at one of two differently colored keys. • The bird got a food reward for a correct response, while an incorrect response resulted in a 30 second time out. • Once the birds had learned to distinguish between 2 and 10 seconds, a 15 second delay in getting the food was introduced for one of the correct answers. • Half the birds had the 2 second stimulus associated with the immediate reward (“short = instant” group) and half had the 10 second stimulus associated with the immediate reward (“long = instant group).

10. Probe trials • Unreinforced probe trials were introduced, making up 2/3 of all trials • Each probe trial had a stimulus that lasted for 2, 3, 4, 5, 6, 7, 8, 9, or 10 seconds • The different probe trials occurred with equal frequency, in pseudorandom order

12. Cage manipulation • During training, birds had been housed individually in cages 44.5 cm high by 75 cm wide by 45 cm deep with water bottles, dwelling perches, and paper lining the floor. • For the cage manipulation, birds were housed 3 to a cage. • In the “standard” treatment, the cage was the same as during training. But, • access to a water bath was unpredictable • the cages were sometimes cleaned with the birds in them • In the “enriched” treatment, the cage was bigger (82 cm by 141 cm by 85.5 cm). Additionally, the birds had: • continuous access to water baths • perches made from natural branches • bark chippings on the floor for the birds to forage in

14. Parameters to be compared • “Bias”: probe value corresponding to 0.5 choice probability • “Sensitivity”: slope of fitted curve • Probability of choosing fast reward option at probe value associated with slow reward • Probability of choosing fast reward option at probe value associated with fast reward

15. Bias Sensitivity In response to probe for delayed reward In response to probe for instant reward

16. p =0.041 Bias Sensitivity p =0.036 In response to probe for delayed reward In response to probe for instant reward p =0.040

17. Discussion • Matheson et al. differs from the Harding et al. paper: • By using a choice procedure instead of a go/no-go procedure. • Both outcomes are rewards, one better than the other. • Tests effect of environmental enrichment. • Depressive realism • Both studies say that these methods help us understand an animal’s experience and can help animal welfare efforts • The results suggest that cognitive bias as a response to stress is a widespread and perhaps primitive trait among animals Side note: rats living in enriched environments don’t get addicted to drugs: http://www.bbc.com/future/story/20130910-drug-addiction-the-complex-truth