Gorillas (Gorilla gorilla gorilla) Fail to Learn Abstract Cues of Differential Outcomes in a Novel Cognitive Bias Test
In order to assess mood state in three male western lowland gorillas housed in a bachelor group, we developed a novel version of a cognitive bias task. The background color of a touchscreen presented a conditional ‘if, then…” rule relating to outcomes involving differential amounts of food rewards. The gorillas struggled to reach a criterion […]
Relative numerousness judgment and summation in young and old western lowland gorillas
The relationship between age, relative numerousness judgment, and summation was investigated in 11 Western lowland gorillas (Gorilla gorilla gorilla). Experiments 1 and 2 evaluated the gorillas’ ability to select the larger of 2 food quantities before and with training. The majority of gorillas did not reliably select the larger quantity in Experiment 1 until receiving […]
Incentive size, food deprivation and food preference
After determining the preferences of rhesus monkeys for 4 foods by a paired-comparison technique, the relative frequency of selection of the most-preferred and the second-least preferred foods were studied when the amounts of each simultaneously presented were systematically varied. Tests were given under 1, 23, and 47 hours of food deprivation. It was found that […]