SAT Reading - Khan Diagnostic Quiz level 3 - reading 21

Many vertebrates and invertebrates show a preferential use

of one side of their body over the other, a phenomenon

known as laterality. Laterality stems from cerebral
_Line lateralization, whereby specific types of information are
₅ referentially processed in one hemisphere of the brain.
It is now widely accepted that brain lateralization conveys

both costs and benefits while performing certain tasks and

that it can have fitness consequences for animals in their

natural environment. Previous studies have demonstrated that
₁₀ strongly lateralized animals perform better than non-

lateralized animals in a variety of contexts. For example,

Magat and Brown found that strongly lateralized parrots

were faster at learning a complex task than non-lateralized

parrots. In addition, strongly lateralized parrots and domestic
₁₅ chickens were faster in discriminating between pebbles and

grains than non-lateralized individuals. Moreover, brain

lateralization is suggested to enhance simultaneous task

performance such as foraging whilst also looking out for

predators. The costs of laterality are various and context
₂₀ specific. For example, strongly lateralized animals often have

difficulty in solving spatial tasks because their inherent turn

bias can be difficult to overcome. Similarly strongly

lateralized individuals perform relatively poorly when they

have to compare similar information in each visual hemifield.
₂₅ The observed pattern of laterality across species, and

particularly the variation within species, is likely shaped by

natural selection to suit contemporary ecological and social

conditions. Large bodied parrots that use extractive foraging

techniques tend to be strongly lateralized whereas small
₃₀ bodied species that graze on grass seeds and nectar are non-

lateralized. In addition, the pattern of lateralization varies

between populations subject to differential predation

pressure. Fish from high predation regions are more strongly

lateralized compared to fish from low predation regions and
₃₅ their pattern of laterality also differs. It has been argued that

fish from high predation locations, or those that readily rely

on schooling, show enhanced laterality so that they can keep

track of their shoal mates and other stimuli simultaneously.
Laterality has been extensively studied using fish as model
₄₀ organisms. A large number of fish species form schools (a

cohesive group of fish that swim in polarized

and synchronized manner) or shoals (a loose social aggregation

of fish). Group cohesion provides advantages by enhancing

foraging success and anti-predator behaviors.
₄₅ It is easy to imagine how such finely tuned maneuvers

could be influenced by laterality. One might predict, for

example, that the stability and the cohesion of a fish school

are preserved if all the fishes tend to swim in the same

direction. Alternatively, perhaps schools are best comprised
₅₀ of a range of lateralized individuals that prefer to take up

different locations within the school. It is possible that fish

with either a right eye or a left eye bias for viewing

conspecifics would be positioned on the left and right side of

the school respectively. This would allow lateralized fish to
₅₅ simultaneously gather information about their school mates

in one hemifield and other key stimuli in the contra-lateral

hemifield (e.g., predators or prey).* In theory, this would

enable them to perform more efficient anti-predator or

foraging behavior due to their ability to process the
₆₀ information more quickly in the appropriate hemisphere.
It is well documented that the position adopted by a fish

when swimming within a school is influenced by a range of

factors, including the internal motivational state (e.g., level

of hunger), hydrodynamics and predator avoidance strategies.
₆₅ Moreover, positions within a school have different costs and

benefits associated with them. For example, peripheral

positions may enhance foraging opportunities, but they are

also more vulnerable to predation. Individuals within

populations vary in their laterality scores and the present
₇₀ study suggests that each fish positions itself within the school

accordingly. Individuals that were more left lateralized when

viewing their mirror image were found in positions at the

periphery of the school keeping the majority of their shoal

mates within their preferred visual field. It is highly likely
₇₅ that this school position is the product of an active choice on

the behalf of the fish which compete for their preferred

positions within the school in a highly dynamic fashion and

is dependent on the laterality scores of the other fish in the

school. It may be that strongly lateralized fish (particularly
₈₀ right biased individuals) benefit from occupying in these

positions but we have yet to conduct tests which involve

predator or prey detection in a schooling context.