I would have to disagree on
Psycho not being a slasher film. The only difference between Scream and Psycho (slasher speaking-wise) is Ghostface wore a mask.
Psycho is
a lot more realstic than most of the slashers out today (Halloween, Friday 13th, TCM, etc).
But the creator of Halloween, Carpenter, said most of Halloween was a tribute or homage, or ideas borrowed from Psycho because its one of his favorite films.
Psycho> inspires slasher HALLOWEEN> Friday the 13th>Scream>etc...
Even the media considers Psycho the first slasher. Here is an article on that:
_________________________
THE SELECTIVE HISTORY OF THE SLASHER FILM
Only in the past decade has the slasher film directed towards innovative trends, violating, for the first time, conventions and mechanisms reused in an uncountable number of films. The slasher film is one of the most structured and concrete film genres.
Recently and particularly the genre has employed post-modernist detachment. This is a particularly laudable diversion, as it occurs in a genre of films known for their similarity. It is evident in two films: The Silence of the Lambs and Scream. The latter preyed on the popular trends of the slasher film genre that went unacknowledged in the entirety of its duration. (Though Scream is the most popular example of this, it was preceded by Wes Craven’s own New Nightmare.) The trick is this: Scream is a slasher film, though in drawing attention to its type it emerges, in some way, as innovative. It is self-aware and -referential, yet is purposefully derivative (and knowledge of the slasher genre will grant the inconsistencies of Scream: foremost, slasher killers have no identity).
The Silence of the Lambs offers one of the most detached perspectives of the slasher film. Firstly, the killer, Hannibal Lector, is not only known but he is studied (this is contrary to established notions of Lector as antihero). But notice the parts of the film that coalesce with slasher methodology: the female survivalist, the sexuality of the crimes; even Lector’s muzzle, only seen briefly in the film, has become a staple method of identifying him. He is not only a horror icon, like other slasher killers, but one of the most recognized.
The final and least laudable trait of the slasher film is its propensity to generate sequels (for measure, the five films mentioned in this article have spawned a combined 18 sequels). Because slasher killers are inhumanly durable, their deaths are never legitimately final.
Slasher films, however derivative and thematically impotent, are generated from a handful of critical successes. The cornerstones of the slasher genre are detailed below.
Psycho
Psycho opens with the caption “Pheonix, Arizona … Friday, December the Eleventh … Two Forty-Three PM.” In this – the first slasher film – the specificity of location lends the film a truth. This convention functions to make otherwise clichéd horror mechanisms seem real, as they are given a ridiculously specific context.
http://www.notcoming.com/features/slasherhistory.html