The Voight-Kampff test was a test used by the LAPD's Blade Runners to assist in determining whether or not an individual was a replicant. The test measured bodily functions such as respiration, heart rate, blushing and pupillary dilation in response to emotionally provocative questions. It typically took twenty to thirty cross-referenced questions to detect a replicant.
Later, Rick Deckard was ordered to perform the test at the Tyrell Corporation by his superior, Harry Bryant, on the Nexus-7, Rachael. With her test, it took over one hundred questions to determine her nature. The reason for this was told to Deckard by Eldon Tyrell, who stated that Rachael was an experimental replicant.
Rachael later asked Deckard if he had taken the Voight-Kampff test, but did not receive an answer, as he was asleep.
Behind the scenes
"A very advanced form of lie detector that measures contractions of the iris muscle and the presence of invisible airborne particles emitted from the body. The bellows were designed for the latter function and give the machine the menacing air of a sinister insect. The VK is used primarily by Blade Runners to determine if a suspect is truly human by measuring the degree of his empathic response through carefully worded questions and statements."
―Blade Runner presskit
The Voight-Kampff machine is perhaps analogous to (and may have been partly inspired by) Alan Turing's work which propounded an artificial intelligence test — to see if a computer could convince a human (by answering set questions, etc.) that it was another human. The phrase Turing test was popularised by science fiction but was not used until years after Turing's death.
The VK test is also strongly reminiscent of the polygraph - a type of lie detector test that measures physiological responses against a pre-established baseline in order to determine whether or not a lie is being told. The line 'Just warming you up, that's all.' spoken by Holden to Leon in the opening scene suggests that a similar baseline is being established.
Also worthy of note is the 'fruit machine', a device developed for use in the Canadian military that aimed to measure pupillary dilation in response to erotic imagery in order to determine whether the subject was homosexual.
The eye footage seen on the machine's screen was stock footage secured from Oxford Scientific. Some actors, such as Brion James, had their own eyes filmed, but for budgetary reasons, it was decided to use only stock footage.