= Mental process
A <mental process> is an activity involved in <cognition>, such as allocating <attention>, interpreting a sensory pattern, retrieving <human memory> or selecting a response. The process is an explanatory construct: a keypress or spoken answer is an observation used to investigate it, not a direct measurement of every internal step.
<Saul Sternberg> tested whether a presented symbol belonged to a short memorized set. His 1966 study found that mean <reaction time> increased approximately linearly with set length and interpreted the pattern in terms of rapid internal comparisons.<High-Speed Scanning in Human Memory by Saul Sternberg>[Abstract; memory-set length, reaction time and serial-comparison interpretation]{ref}
An invented model illustrates the reasoning. Suppose $T(n)=a+bn$, where $n$ is set size, $a=300\,\mathrm{ms}$ and $b=40\,\mathrm{ms}$ per item. Then $T(2)=380\,\mathrm{ms}$ and $T(5)=500\,\mathrm{ms}$. The intercept can summarize operations whose duration does not vary with $n$, while the slope summarizes the measured size effect. These values are illustrative, not Sternberg's reported estimates.
A good fit establishes a pattern that a proposed <mental process> can explain; it need not uniquely establish that process. Changes in <attention>, response strategy or other operations may also affect <reaction time>. Comparing predictions across controlled conditions makes the inference stronger than naming an internal activity after one measured response.
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