4. A computer-implemented method comprising: as implemented by one or more computing devices configured with specific executable instructions, receiving a request for output of audio content; in response to the request for output of the audio content: retrieving, from one or more data stores, companion content associated with the audio content, the companion content including textual content representing words spoken in the audio content; determining a first keyword associated with a first portion of the textual content; determining a second keyword associated with a second portion of the textual content; retrieving, from one or more data stores, a first visual content item associated with the first keyword and a second visual content item associated with the second keyword; and causing presentation of the first visual content item and the second visual content item during output of corresponding portions of the audio content, such that (a) the first visual content item is presented during output of an audio content portion corresponding to the first portion of the textual content and (b) the second visual content item is presented during output of an audio content portion corresponding to the second portion of the textual content.
5. The computer-implemented method of claim 4 , wherein the first visual content item comprises at least one of an image or a video.