PC Therapist

What it is

PC Therapist is a conversational computer program written by Joseph Weintraub. A modified version of the program won the first annual Loebner Prize Competition on November 8, 1991 ^[1]. In that competition, PC Therapist fooled five of 10 judges into thinking it was human ^[1]. The result is the central documented outcome for the program: a software system whose replies were accepted as human by half of the judges in that contest ^[1].

Origins

At the time of the contest, Weintraub was president of Thinking Software, Inc. of Woodside, New York ^[1]. He was 48 years old and had spent more than three years writing PC Therapist ^[1]. His work included designing and selling artificial intelligence, expert systems and natural languages software ^[1]. PC Therapist therefore came from a software company whose president worked on AI and language-related products, and the program was the product of a multi-year writing effort ^[1].

How it worked

Weintraub limited the program's contest topic to whimsical conversation ^[1]. The program used five megabytes of memory and a knowledgebase of thousands of amusing quotations and rules for conversation ^[1]. It ran on any IBM compatible computer ^[1]. The report lists memory use, knowledgebase size and hardware compatibility as the program's technical details, alongside the topic restriction ^[1].

A conversational program with this design can produce plausible replies without building a full model of the world. It can store a collection of quotations and a set of rules for choosing when to use them. The rules can be simple patterns: if the input contains a certain cue, choose a quotation or a response of a certain type. In PC Therapist, the report describes a knowledgebase of thousands of amusing quotations plus rules for conversation ^[1]. The topic restriction also matters: the program was not asked to converse about any subject, but to stay within whimsical conversation ^[1]. That makes the contest result narrower than a general claim about open-ended conversation ^[1].

What the judges saw

The judges' task was to decide whether the entity producing the replies was human; five of 10 decided that it was ^[1]. The score records those five judgments, not a claim that every judge was fooled ^[1]. For a conversational program, the contest produced a bounded result: within a limited topic, a set of judges heard replies they took to be human ^[1].

Place in development

The Computer Museum report records PC Therapist as the winner of the 1991 Loebner Prize Competition ^[1]. Its documented features are a knowledgebase of quotations and conversational rules, a five-megabyte memory footprint, and compatibility with IBM compatible computers ^[1]. The program was limited to whimsical conversation in the contest ^[1]. Weintraub, its author, was president of Thinking Software and had worked on AI, expert systems and natural languages software ^[1].

In the record of conversational programs, PC Therapist belongs to the line of systems that combine a store of prepared text with rules for conversation. The report's account shows that design at work in a public contest: stored quotations and conversational rules, a fixed topic, and a result based on judges' human-or-machine decisions ^[1].