Methodological problems in AIDS behavioral research: influences on measurement error and participation bias in studies of sexual behavior

An unprecedented number of human sexuality studies have been initiated in response to the acquired immune deficiency syndrome (AIDS) epidemic. Unfortunately, methodological developments in the field of sex research have been slow in meeting the demands of AIDS investigations focusing on the diverse populations at risk for infection with the human immunodeficiency virus (e.g., adolescents, gay men, intravenous-drug users, ethnic minorities, elderly transfusees). In this article, we review and integrate current literature on measurement error and participation bias in sex research, with an emphasis on collecting sexual information in the context of AIDS. The relevance of these findings for AIDS-related sex research is discussed, and recommendations are made to guide future investigations.     

Freedom and knowledge: an experimental analysis of preference in pigeons

Relative responding in initial links of concurrent-chain schedules showed that pigeons preferred free to forced choices and informative to uninformative stimuli. Variable-interval initial links on two lower keys (white) of a six-key chamber produced terminal links on either two upper-left keys (blue and/or amber) or two upper-right keys (green and/or red). Terminal.links in which pecks on either of two lit keys produced fixed-interval reinforcement (free choice) were preferred to links with only one lit fixed-interval key available (forced choice). Terminal links with different key colors correlated with concurrent fixed-interval reinforcement and extinction (informative stimuli) were preferred to links with these schedules operating on same-color keys (uninformative stimuli). Scheduling extinction for one of the two free-choice keys assessed preference for two lit keys over one lit key, but confounded number with whether stimuli were informative. Fixed-interval reinforcement for both keys in each terminal link, but with different-color keys in one link and same-color keys in the other, showed that preference for informative stimuli did not depend on stimulus variety. Preferences were independent of relative responses per reinforcement and other properties of terminal-link performance.     

Autoshaped responding: A baseline for studying stimulus preference

In an autoshaping procedure with pigeons, trials consisted of the illumination of two keys, each with a different color, and then a response-independent feeder operation. Over successive conditions, all key-color pairs were arranged from the set of amber, red, green, and blue lamps. During sessions with a given pair, the left-right configuration of the colors varied irregularly, and the two colors alternated in illuminating the feeder. With one red and one green key, for example, red appeared sometimes on the left and sometimes on the right, and the feeder was alternately lit red or green on successive trials. Both total pecks and proportion of trials with at least one peck on a key of a given color were generally greater for red and amber than for green and blue, and relations among preferences were generally transitive across different color pairs. Repeating the procedure with decreased red and amber intensities and increased green and blue intensities reduced red and amber pecking relative to green and blue pecking, implying that differences in responding were determined more strongly by intensive than by chromatic properties of the stimuli.     

Uninstructed human responding: sensitivity to ratio and interval contingencies

College students' presses on a telegraph key were occasionally reinforced by light onsets in the presence of which button presses (consummatory responses) produced points later exchangeable for money. One student's key presses were reinforced according to a variable-ratio schedule; key presses of another student in a separate room were reinforced according to a variable-interval schedule yoked to the interreinforcement intervals produced by the first student. Instructions described the operation of the reinforcement button, but did not mention the telegraph key; instead, key pressing was established by shaping. Performances were comparable to those of infrahuman organisms: variable-ratio key-pressing rates were higher than yoked variable-interval rates. With some yoked pairs, schedule effects occurred so rapidly that rate reversals produced by schedule reversals were demonstrable within one session. But sensitivity to these contingencies was not reliably obtained with other pairs for whom an experimenter demonstrated key pressing or for whom the reinforcer included automatic point deliveries instead of points produced by button presses. A second experiment with uninstructed responding demonstrated sensitivity to fixed-interval contingencies. These findings clarify prior failures to demonstrate human sensitivity to schedule contingencies: human responding is maximally sensitive to these contingencies when instructions are minimized and the reinforcer requires a consummatory response.     

Independence of concurrent responding maintained by interval schedules of reinforcement

A pigeon's responses were reinforced on a variable-interval schedule on one key; and, concurrently, either a multiple or a fixed-interval schedule of reinforcement was in effect on a second key. These concurrent schedules, conc VI 3 (mult VI 3 EXT) or conc VI 3 FI 6, were programmed with or without a changeover delay (COD). Because the COD provided that responses on one key could not be followed by reinforced responses on the other key, responding on one key was not likely to accidentally come under the control of the reinforcement schedule on the other. When the COD was used, the performances on each key were comparable to the performances maintained when these interval schedules are programmed separately. The VI schedule maintained a relatively constant rate of responding, even though the rate of responding on the second key varied in a manner appropriate to the schedule on the second key. The mult VI 3 EXT schedule maintained two separate rates of responding: a relatively high rate during the VI 3 component, and almost no responding during the EXT component. The FI schedule maintained the gradually increasing rate of responding within each interval that is characteristic of the performance maintained by this schedule. The concurrent performances, however, did include certain interactions involving the local characteristics of responding and the over-all rates of responding maintained by the various schedules. The relevance of the present findings to an inter-response time analysis of VI responding, a chaining account of FI responding, and the concept of the reflex reserve was discussed.     

Interocular transfer of discriminations in the pigeon

Pigeons with one eye covered were trained to discriminate intensities or colors of stimuli located to one side of the head, or intensities, colors or forms of stimuli located in front of the beak. Each discrimination transferred to the covered eye, even when previous training with the covered eye included the reversal of the tested discrimination. Pigeons also were able to learn conditional discriminations in which appropriate responding depended on which eye was covered.