WHEN SIGMUND FREUD initially began inquiring into the nature of the human psyche, contemporaries passed him off as a sexual crackpot. And while many psychologists today are still wary of reducing all behavior to id, ego and superego, most professionals in the field concede that repressed behavior is fundamental to a well-functioning society.

The artistic response to Freud's theories has enabled film directors to have a field day with movies exploring the human psyche. Hitchcock flicks have carved a niche for themselves in cinematographic history and the Dr. Jekyll and Mr. Hyde school of screenplay has enabled writers like Steven King to probe the inner regions of the mind.

Graham Baker's latest film, Impulse, is yet another in the endless line of psychological thrillers to hit the screen. And, as with its predecessors, the title alone would make Freudians turn over in their graves.

From the steamy promotional material to the film's none too subtle previews, Impulse would appear to possess all the necessary credentials to qualify as a low-budget fleshbath. Yet from its outset, the film works to counter that temptation. In fact, with the exception of one brief sex scene, ironically distinguished by its lack of nudity, sex is essentially absent from this film.

Moreover, Impulse successfully sets itself apart from ordinary thrillers by legitimately developing its plot and characters. For the most part, the characters in this film come across as real, and if the acting is somewhat nondescript, the tempo at least keeps things from getting dull. In fact, because relationships and conflicts crop up so intensely fast, it is easy initially to mistake Impulse for a drama rather than a psychological thriller.

At the outset, director Baker craftily disguises the plot beneath the cloak of family tragedy. Jennifer (Meg Tilly), a small town ballerina, has gone to study dance in New York, where she meets her soon-to-be boyfriend Stuart (Tim Matheson). Stuart is a cultured yuppie finishing up his medical residency. Yet no sooner do Jennifer and Stuart become involved, than Jennifer's mother discovers the romance, and during an accusatory phone call, shoots herself. Jennifer and Stuart race home to the rural Midwestern town where Jennifer's mother lives, and the plot quickly takes on a surreal glaze.

At first, the couple ignores a series of bizarre, mildly violent actions by the locals. Jennifer doesn't give much thought to a friend's remark not to touch her because "something's wrong with her." Nor is she troubled by the unusually heated quarrels between her father and brother. But the incidental occurrences begin to follow a menacing pattern: An irate motorist trashes Stuart's car, a rejected suitor smashes his own hands.

What follows is a predictably heroic attempt by Stuart--the educated, urbanized outsider--to save the town from itself. He suspects that a toxic substance is causing the townspeople to repress the emotional mechanism designed to curb passions, literally lifting the lid off the id. His discoveries come--unsurprisingly--too late. The film's closing minutes play like a spinoff of The Stepford Wives.

While Impulse succeeds in maintaining a compelling level of suspense, it falls short of realizing its potential as a creative thriller--largely because it does not finish what it begins. While the characters start off as realistic, the film leaves them caught up in unresolved dilemmas. And even though the anonymity of the small town setting works well for the film's rather fantastic premise--the small size permits the evil to permeate completely--it also turns the characters into stock types by the film's end.

Impulse falls short of becoming the crafty psychological exploration it starts out as, because the impetus for evil stems from external factors. It is chilling to watch neighborhood kids ignite Jennifer's car with gasoline, but the incident somehow loses its impact when we discover that their action comes as the result of a carton of contaminated milk. In this light as well, the film's political plugs for environmentalism detracts from its force as a psychological thriller.

As a social statement and character study, then, Impulse stumbles. As a visual collage of human evil and a psychological work of suspense, it succeeds, and occasionally even sparkles. It is the product of a rich, but imperfect collective creative psyche.