Self-administration of surveys has been shown to increase respondents’ reporting of sensitive information, and audio computer-assisted self-interviewing (ACASI) has become the self-administration method of choice for many social surveys. The study reported here, a laboratory experiment with 235 respondents, examines why ACASI seems to promote disclosure. It compares responses in a voice-only (self-administered) interface with responses to a face-to-face (FTF) human interviewer and to two automated interviewing systems that presented animated virtual interviewers with more and less facial movement. All four modes involved the same human interviewer’s voice, and the virtual interviewers’ facial motion was captured from the same human interviewer who carried out the FTF interviews. For the ten questions for which FTF-ACASI mode differences (generally, more disclosure in ACASI than FTF) were observed, we compared response patterns for the virtual interviewer conditions. Disclosure for most questions was greater under ACASI than in any of the other modes, even though the two virtual interview modes involved computerized self-administration. This suggests that the locus of FTF-ACASI effects is particularly tied to the absence of facial representation in ACASI. Additional evidence suggests that respondents’ affective experience (e.g., comfort) during the interview may mediate these mode effects.