An audio-visual suggestion received by Spock
Audio-visual suggestion was a suggestion that was made through audio-visual means.
When the male crewmembers of the USS Enterprise were under the spell of the female inhabitants of the second planet of the Taurean system in 2269, the ship received a subspace radio signal from the planet sent by an opto-aud.
To Spock, it was identified as the sound of a Vulcan marriage drum, followed by an audio-visual suggestion of the female who was playing it. (TAS: "The Lorelei Signal")