A prima vista
Played from sight, without prior practice.
What it means
A prima vista means “at first sight” and denotes playing or singing from the page: a notated text is performed without having practised it beforehand. In English one speaks of sight-reading or sight-singing, in French of à vue.
Sight-reading is to be distinguished from improvisation. There the music is invented in the moment; here an existing text is read and realised in the moment. It is likewise to be kept apart from playing from memory, in which the text has already been internalised.
The expression also denotes a skill that is specifically practised in musical training and that belongs to the craft of répétiteurs, orchestral musicians and accompanists.
In the notation
As a playing instruction in the score the phrase is not in use; it describes a situation, not a manner of performance. It is common, however, in teaching and in music publishing, as a label for sight-reading practice material and for easy pieces meant to be playable without preparation.
Musical use
Sight-reading has always belonged to professional practice. In times when music was written predominantly for immediate use, it went without saying that musicians performed unfamiliar pieces straight away. Today too it is an everyday matter in orchestral service, in song accompaniment and in church music. In competitions and entrance examinations it forms a task of its own.
Music psychology has measured reading ahead. In 1974 John Sloboda transferred a method from reading research to sight-reading: the score is unexpectedly hidden during playing, and the number of notes still played correctly afterwards gives the eye-hand span. Later studies consistently confirm that skilled sight-readers read further ahead than less skilled ones.
Performance practice
Before the first note, gain an overview: key, time signature, tempo, striking passages, repeat marks. Choose a tempo you can hold at the hardest passage, not at the beginning. Read ahead — the eye should always be a bar further on than the hands. And keep the pulse going even when notes are missing: playing on matters more than completeness.