Neurobehavioral Assessments of Cerebral Vasospasm - Animal Models of Acute Neurological Injuries: Injury and Mechanistic Assessments - page 561

In the Same/Different tasks, the two (or more) stimuli can be
shown simultaneously or sequentially. In the latter case, visual
memory can be tested since a sample stimulus is fi rst presented,
followed by a delay, and then the test stimulus, after which the
monkey responds. The Go/No-Go and Same/Different procedures
can also be used to test object recognition and categorization abili-
ties, which are discussed in Sect. 7.4. below.

7.2. Posterior Parietal
Cortex

To study potential damage to areas of posterior parietal cortex
(PPC), example tasks include those that measure (a) attention,
(b) object location and visual neglect, (c) sensorimotor integration,
and (d) both perception-based and reward-based decision making.
Classic tests of spatial attention include cuing tasks ( 205, 206 ).
In these tasks, monkeys are trained to fi xate a cue in the middle of
a visual display. When a target appears anywhere in the visual dis-
play, they must saccade to it as quickly as possible to receive a juice
reward. To manipulate attention exogenously, i.e., refl exively,
before the target is displayed, a temporary cue is presented near the
location of the subsequent target. This cue refl exively draws the
monkeys' attention to the target area, causing them to be quicker
to respond to the target once it appears. This shortened response
time due to attentional enhancement by the cue can also be com-
pared to the negative effects of displaying the cue in the wrong
location. Since attention is directed at the invalid location, subjects
are slower to respond to the valid location.
Endogenous attention can also be tested using the cuing task,
whereby arbitrary symbols, such as arrows, are used as cues to direct
attention to various locations in the visual display. For example, an
arrow pointing left, displayed just above the fi xation point, would
direct attention to the left, which would enhance responses to the
left and interfere with responses required to the right. Monkeys
must fi rst be trained to learn that the arbitrary cues, such as arrows
or a red versus blue square, predict subsequent target locations.
Other classic tests of attention include visual search tasks
( 207 ). In these tasks, subjects again fi xate a central stimulus, and
several items are placed throughout the display. A go cue, such as
elimination of the fi xation point, instructs the monkeys to search
for the target that is different from the others as quickly as possible.
Once this item is found, the monkeys must saccade to the target.
When the target differs in one dimension from the “distracter”
items, such as in color, the target tends to pop out refl exively from
the others. However, when the target item differs from the others
in more than one dimension, such as both in color and shape, it
appears to require a serial search for the target, resulting in a much
longer reaction time that is linearly related to the number of
distracters. Damage to PPC can be measured by comparing the
performance of these monkeys to that of monkeys without such
damage or to performance prior to cortical damage.