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DISCRIMINATION OF QUANTITY IN A CALIFORNIA SEA LION

Michael Noonan, Eric Gaglione, Pamela Prowten, Katherine Karlis and Rebecca Russo

Canisius College and the Aquarium of Niagara Falls, New York

Presented at the American Psychological Association, Toronto, Ontario, August, 1996.

INTRODUCTION

There has been increasing interest in the ability of non-human animals to process information normally associated with human cognition (e.g., Roitblat, 1993). Our interest in the present study was to assess the ability of a California sea lion (Zalophus californianus) to process the "concept" of quantity.

It can be reasoned that it would make ecological sense for an animal like a sea lion to be able to distinguish a greater from a lesser number of objects. When a sea lion is pursuing fish, it would presumably be adaptive for it to be able to assess the relative quantity of fish present in different directions as part of its effort to maximize its intake of food.

In the present experiment, we presented a single captive sea lion, Zalophus californianus, with paired stimuli and consistently rewarded the her for choosing the stimulus with the greater number of dots.

PROCEDURE

The subject of this study was a eight-year-old, female California sea lion which had been born and raised in captivity. Testing for this project took place over 128 consecutive days. Testing was conducted on a 12 m² platform adjacent to a 400,000 liter pool. Testing commenced at 8 am each day and the fish rewards associated with testing constituted the first food following a 12 hour overnight fast. Her weight fluctuated between 81.0 kg and 85.5 kg.

At the outset of this study, the subject was shaped (using fish reinforcement) to touch her nose to a plastic stimulus card holder. Thereafter, she was presented with pairs of black and white cards and allowed to touch her nose to whichever one she chose. Correct responses were reinforced with fish; incorrect responses were punished with ice. (Prior to this study, the sea lion was observed to apparently dislike ice. That is, when given an ice cube in place of a reinforcing fish, she would spit out the ice or even refuse to take it. In this study, incorrect responses were "reinforced" with ice cubes presented as if food.)

Between testing trials, the subject was taught to remain on a pedestal, and was allowed to observe the investigator manually place 8.5 x 11 in. stimulus cards 2 m to the left and right of the pedestal. After placing the stimuli, the investigator moved behind the sea lion and gave a voice command releasing the subject to select a stimulus. The sea lion then left the pedestal and indicated its choice by touching one of the cards with its nose, whereupon the appropriate sound ("chirp" for correct; "bzzz" for incorrect) was emitted to indicate to the sea lion that the behavior was completed. The food (or ice) was then given to the sea lion.

The side on which each quantity of dots in any pair was placed, and the order in which they were placed, were varied pseudorandomly and counter-balanced across trials. To guard against the possibility that the sea lion might base its distinction on the overall luminance of the stimuli, we varied the size of the dots from trial to trail, and we counterbalanced the trials so that in any block approximately equal numbers of trials were included in which the overall luminance ratio between the greater quantity and lesser quantity of dots on the stimulus card was greater, equal, or less than one. To guard against the possibility that the sea lion would base its discrimination on the position of the dots on the stimulus cards, or on the pattern which they presented, we also varied the position of dot placement from trial to trial.

Testing took place in blocks of 20 trials. Each trial consisted of a paired choice, and in every instance, the sea lion’s task was to choose the stimulus card with the greater number of dots. Over a period of days, testing focused exclusively on a single numerical pair (e.g., 2 vs 3) until the subject reached a criterion of 90% correct response within any 20 trial block.

Our focus was on testing the animal’s ability to discriminate quantity pairs separated by only one dot (i.e., 1 vs 2, 2 vs 3, 3 vs 4, etc.), and these pairs were tested in ascending order. Before testing each pair, we presented the sea lion with successive approximations of the task by introducing each new "low number" to the sea lion in blocks of trials in which it was compared to 10, then 8, 6, etc. The tests moved to the next approximation only when the sea lion made 18/20 correct responses.

RESULTS

Generally speaking, the sea lion was reliably able to discriminate the larger quantity on most trials. Over the entire five month study period, she chose the correct card on 2049 (76.4%) of 2680 trials. She also showed similar accuracy for most of the seven critical pairs upon which we focused:

DISCUSSION

Our sea lion was clearly able to visually distinguish close differences in quantity up to the comparison 6 vs 7. This result is comparable to what has been reported for chimpanzees in a somewhat similar test (Rumbaugh et al, 1987).

It will be noted that the subject’s highest accuracy was in the low middle range of quantities tested, with maximum accuracy for 2 vs 3. We suspect two factors influenced her performance to produce these results. We attribute her improving scores as she progressed from 1 vs 2 to 2 vs 3 as likely due to an increasing familiarity with the task. We presume that her subsequent decrease in accuracy was due to the greater difficulty of higher order comparisons.

It will be interesting in future studies to probe the ecological significance of the sea lion’s quantitative abilities, and ask in future experiments whether the discrimination of quantity plays a role in the pursuit and capture of prey.

REFERENCES

Roitblat, H.L., Herman, L.M. & Nachtigall, P.E. (Eds) Language and Communication: Comparative Perspective. Hillsdale, NJ: Lawrence Erlbaum, 1993.

Rumbaugh, D. M., Savage-Rumbaugh, E.S., and Hegel, M. (1987) Summation in the chimpanzee (Pan troglodytes). Journal of Experimental Psychology: Animal Behavior Processes, 13, 107-115.