Breakdown of Sofort ändert sich die Wahrnehmung.
sofort
immediately
sich
oneself / himself / herself / themselves (reflexive pronoun)
ändern
to change (modify, alter)
die Wahrnehmung
the perception
Questions & Answers about Sofort ändert sich die Wahrnehmung.
Why does sich come before the subject die Wahrnehmung here?
In German word order, when the subject is pushed after the verb (because an adverb like Sofort is in position 1), a reflexive pronoun like sich comes before the subject if that subject is a noun. If the subject were a pronoun, the order would flip: Sofort ändert sie sich.
Is it grammatically wrong to say: Sofort ändert die Wahrnehmung sich?
While you might occasionally hear that order in casual speech, standard German strongly prefers the reflexive pronoun sich to come directly after the finite verb whenever the subject is a full noun phrase rather than a pronoun.
Does the verb ändern always require the reflexive pronoun sich?
Not always. It depends on whether there is a direct object. When a subject changes on its own (like perception changing), you use the reflexive form sich ändern. If someone is changing something else, there is no reflexive pronoun. For example: Er ändert den Plan (He changes the plan).