PRIMATES,27(1): 63--82, January 1986 63 Infant Stumptailed Macaques Reared with Mirrors or Peers: Social Responsiveness, Attachment, and Adjustment JAMES R. ANDERSONa n d ARNOLD S. CHAMOVE University of Stirling ABSTRACT. Comparisons of activity toward mirrors and peers in infant macaques being reared with one of these stimuli as the primary rearing partner revealed markedly greater social responsive- hess to a fully accessible cagemate than to one's own reflection. Measures of exploration, aggression, and especially play all revealed the cagemate to be the more potent social stimulus. Mirror-reared in- fants given additional experience of a live peer behind a transparent partition ~ere less responsive to the mirror than were infants with no social stimulation other than a mirror. In contrast, cagemate- directed behavior of peer-reared infants ~xas not seriously affected by additional exposure to a mirror. A fully accessible peer also elicited more social responding than a peer behind a transparent parti- tion, and infants with experience of both a live cagemate and mirrors were generally more respon- sive toward the former. Greater agitation in peer-reared than in mirror-reared stumptailed mon- keys during separations from their rearing partners suggests that exposure to the physically ac- cessible partner led to stronger attachments. Infants reacted positively to a moderately unfamiliar environment but showed behavioral disruption when placed in a very unfamiliar environment. Dis- ruption was especially evident in peer-reared infants, in x~hich exposure to the unfamiliar environ- ment was compounded with the absence of the attachment figure. Mirror-rearing appeared to reduce the tendency toward 'isolation syndrome" behaviors compared to alone-rearing, and these behaviors appear to be less common in stumptailed than in rhesus macaques. Key Words: Monkeys; Social development; Attachment; Mirror; Contact. INTRODUCTION Since the now classic account by HARLOW and ZIMMERMAN (1959) of the role of 'contact comfort' in the development of infant-mother attachment in rhesus monkeys, various studies have examined the role of different modalities in early primate social interactions. For example, experimental manipulations have defined more clearly the textural qualities allow- ing surfaces to elicit filial responses (HARLOW& Svoul, 1970). The channel that has received most attention is vision. SACKEa-a" (1966) reported that during rearing in total social isola- tion, infant rhesus monkeys were more responsive to projected pictures of monkeys than to pictures of inanimate objects, suggesting art important role for visual cues in eliciting early social responses. Subsequent experiments confirmed attachments following early visual exposure to social objects (see CAmNS, 1966; CHAMOVE & HARLOW, 1975; SACKETT & RUPPENTHAL, 1973), though visual contact is not essential (CHAMOVE, 1984). Monkeys respond to their reflections in a mirror with social displays including submission, aggression, affiliation, and play (ANDERSON, 1984; GALLUP, in press), and, unlike chimpan- zees and orangutans, show no indication of self-recognition (reviews: ANDERSON, 1984; GALLtSP, in press). This social orientation persists, although overt responses may wane with