Theoretical interpretation  

According to Greenwald, the IAT provides a "window" into a level of mental
operation that operates in unthinking (unconscious, automatic, implicit,
impulsive, intuitive, etc.) fashion because associations operating without
active thought (automatically) can help performance in one of the IAT's two
"combined" tasks, while interfering with the other. Respondents to the IAT
experience a higher (conscious, controlled, explicit, reflective, analytic,
rational, etc.) level of mental operation, when they try to overcome the
effects of the automatic associations. The IAT succeeds as a measure because
the higher level fails to completely overcome the lower level.  [33]

The interpretation that the IAT provides a "window" to unconscious mental
contents has been challenged by Hahn and colleagues, whose results indicated
that people are highly accurate in predicting their own IAT scores for a
variety of social groups.  [34]

De Houwer theorizes that the IAT is a measure of a response compatibility
effect, in which participants first learn to associate positive and negative
words and concepts with pressing specific keys on the keyboard. Later in the
test, when participants are instructed to sort words and concepts that are
both negative and positive with the same keyboard key, De Houwer argues that
much of the latency and incorrect responses that result from this change are
due to the increased cognitive complexity of the task, and not necessarily a
reflection of implicit bias.  [14]  [35]

Brendl, Markman, and Messner have proposed a random walk model process to
explain responses in the critical portions of the IAT. They theorize that test
respondents base their responses on a process of mental evidence-gathering
that continues until the evidence for one option or the other (right or left
key) reaches a threshold, at which time a decision is made, and action is
taken. This requires consideration of both the concept and the attribute,
which can be congruent or incongruent - all factors that affect decision
speed. All evidence during the compatible block of the test is congruent,
allowing for fast decision-making. However, incongruent concept and attribute
in the incompatible task leads to longer processing time. Increased task
difficulty also increases evidence threshold criterion, further decreasing
decision speed.  [14]

An alternative or complementary theory from Mierke and Klauer holds that the
cognitive control processes required to switch back and forth between
categorizing based on concept versus based on attribute leads to reduced
speeds in the critical blocks of the test. In other words, it is much less
mentally demanding to sort concepts in the compatible block when only one
aspect of the concept must be focused upon. Comparatively, sorting concepts in
the incompatible block, which requires focusing on both concept and attribute
not only takes longer to process because of the increased complexity, but also
because the previous concept may have required a different cognitive effort.
[14]

Finally, Rothermund and Wentura propose a figure-ground model of explanation
for the IAT. In essence, this theory suggests that IAT respondents simplify
their task by relying on salience. For example, negative is salient for most
people, so if a respondent is to press the right key for negative words, the
individual will plan to press the right key for all negative words (figure),
and the left key for any other (non-negative) words (ground). This leads to
fast decision-making in the compatible task and two of the critical tasks, but
not for the third critical task, in which two salient categories require
different keys pushed.  [14]

There is empirical support for all these explanations of the IAT's effects,
but this is not necessarily evidence against the IAT's overall validity, as
these theories are not mutually exclusive. Furthermore, regardless of the
fundamental cognitive processes of the IAT, studies show that multiple
implementations of the test validly measure their targeted constructs, and the
psychometric value of each implementation varies as a function of its
individual characteristics (e.g., construct measured, participant
characteristics, testing environment).  [14]  [36]