Long Term Memory, Attention and Sensory Perception of Dolphins

Introduction

Cognition is the understanding and development of mental processes through senses and experiences to obtain knowledge. The areas of cognition in bottlenose dolphins (Tursiops truncates) I will be exploring are: long term memory, attention and sensory perception. Early interest in bottlenose dolphin cognition arose from its large brain to body ratio (Herzing and Johnson, 2015) and recent studies have revealed their vast cognitive abilities which are continually being researched. In this review I aim to explore the available literature surrounding cognition in bottlenose dolphins and identify areas where future research should be focused.

Long Term Memory

Earlier studies of dolphin memory have concentrated on working memory, where information is stored for a short amount of time. Whereas recent studies such as ‘Decades-long social memory in bottlenose dolphins' (Bruck, 2013) explore the long-term memory of dolphins. In this study 43 dolphins with varying ages were tested through the use of signature whistles, which are calls unique to each dolphin. The dolphins had previously lived together but had been separated for an average of 6 years.

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Underwater speakers played habituation noises with random whistles played in the intervals until the dolphin ignored the noises for 30 seconds. Familiar and unfamiliar whistles then replace the random whistles and the reactions of the dolphins were recorded. Reactions included head turning towards the speaker, approaching the speaker and forceful contact to the speaker or rapid swimming. The results showed a significantly greater response to familiar whistles and the level of response was not altered by separation length (Bruck, 2013). The habituation sounds, and random whistles mean that any reaction was likely due to memory and not the novelty of the sounds or speakers, and the large sample size means that is it unlikely that the results are due to chance.

Although dolphins in captivity would have fewer dolphins to remember so may perform better in this task than wild dolphins. Memory is very important in cognitive function and a dolphin's long-term memory can be useful in storing motor skills and identifying threats and alliances (Herzing and Johnson, 2015).

Attention

Attention involves the continuous concentration on an object or task whilst distractions and unneeded information is ignored. In Ridgway's journal ‘Dolphin continuous auditory vigilance for five days' a male and females' attention was tested by the use of two 70kHZ sounds and a 0.5 second distractor sound played every 30 seconds. The distractor sound was replaced by a 1.5 second target sound which was played randomly between four and 24 minutes. The dolphin received a reward when the paddle was pressed within 21 seconds of hearing the target sound. The dolphins were tested up to 120 hours at a time with high performance levels which were over 94% for both dolphins (Ridgway, 2006). This is confirmation that dolphins are able to maintain attention for prolonged periods of time as the target sound was unpredictable. Although only two dolphins were tested so the data collected is not representative of the whole population. It also supports the idea that dolphins are able to rest each hemisphere of their brain separately (Ridgway, 2002), this allows the dolphin to remain aware of its environment and attentive to dangers whilst it rests (Ridgway, 2006).

Sensory Perception

Perception involves the analysis of information through the senses to more clearly understand the surrounding environment. Sensory perception in dolphins mainly involves echolocation and vision, with the main area of focus being how dolphins are able to perceive objects using both of these senses. In ‘The object behind the echo: dolphins (Tursiops truncates) perceive object shape globally through echolocation' (Pack et al, 2002). In this experiment the dolphin was either shown an object visually whilst it was held in the air (dolphin echolocation is not effective in air) or suspended in opaque boxes which allowed echolocation. The objects shown were different shaped but some shared similar features. The dolphins had to pick a match between three objects or could press a response paddle if none of the objects matched. Matches were found to be correct on 93% of vision- echolocation trials and 99% of echolocation- vision trials. These results tell us that dolphins are able to use their echolocation to look at an object as a whole rather than just its features. Complex shapes that had not before been seen by the dolphin were used which means that the dolphin did not match the shapes through associative learning (Herzing and Johnson, 2015). Although only on dolphin was tested which limits how useful these results are as it is not representative of the whole population.

Opposition

There are some alternative theories as to why dolphins have such a large brain to body ratio. Some believe that dolphins large brain size is entirely due to echolocation and the cognitive needs that this has (Marino et al, 2007). Another theory is that dolphins have large brains due to the selection pressure of low water temperatures, as having a larger brain counteracts the heat loss as the brain is thermogenic. (Manger, 2006). These theories are less researched and not widely accepted due to the copious evidence available displaying the highly complex behaviours that dolphins are capable of.

Conclusion

In this review I have explored three major areas of dolphin cognition; long term memory, attention and sensory perception. From this review I have found that dolphins have the capability to follow out highly complex behaviours, and despite other theories I believe that this is the reason for their large brain to body ratio. From the literature I have reviewed I can conclude that the future research into dolphin cognition should focus on evidence of cognition in wild dolphins, and further research should be carried out in sensory perception and attention using a larger sample size in order to achieve more representative results.