Spatial and physical frames of reference in positioning a limb

Splints attached to the right forearm were used to rotate the forearm’s physical reference frame, as defined by the eigenvectors of its inertia tensor, relative to its spatial reference frame. In two experiments, when subjects were required to orient the forearm parallel to, or at 45° to, the environmental horizontal, they produced limb orientations that were systematically deflected from the forearm’s longitudinal spatial axis in the direction of the forearm’s physical axes. The position sense seems to be based on inertial eigenvectors rather than on joint angles or gravitational torques.     

A comparison of attentional and control shift models of the performance of concurrent tasks

A concurrent verbal task was superimposed upon the performance of a practiced bimanual motor skill by right-handed Ss. Addition of the verbal task did not increase the total number of errors; however, a significant interaction between hands and conditions was observed. The right hand made significantly more errors under the verbal condition, while the left hand made non-significantly fewer errors under that condition. These findings were interpreted as supporting an attentional model rather than a model which proposes that addition of the verbal task causes control of the right hand to shift to the non-verbal right hemisphere.     

Mental search processes in problem solving

A new approach to problem solving was applied to multisolution problems in a memory search task. Subjects memorized a list of eight four-letter foods, and then searched mentally through the list for answers to questions. The times between successive answers (IRTs) were recorded along with the answers themselves. This allowed a comparison of two possible memory search strategies: (1) sampling with replacement, and (2) sampling without replacement. The results were largely in agreement with the sampling-without-replacement strategy. However, a more detailed breakdown of the data revealed that most subjects searched through the list in a rigid serial order. Further, an analysis of questions with identical answers showed that the IRTs were very nearly additive. This led to an additive time component model based on the independent summation of (a) read-in time, (b) memory-search time, (c) decision-making time, and (d)response-output time. This approach appeared generally more satisfactory than previous attempts to account for problem-solving behavior.     

APE: average potential evaluation software for the LAB-8 system

A paper-tape software system is described which allows the addition and/or subtraction of signal averaging data from the DEC advanced averager program. This pooled averaging data may be plotted, printed, or punched. A DEC LAB-8 system with 4K memory and high-speed reader/punch are required. Several examples of the application of the system to human evoked brain response data are presented, and the application of the system to other problems is discussed.     

Control of avoidance by a response-produced stimulus

Three pigeons were trained to press a foot pedal to postpone electric shock. The safety signal was a tone of 1000 Hz, which sounded for 5 sec following each press; silence therefore served as a warning signal. After the performance approached asymptote, test sessions were interspersed among the training sessions. Following a warm up, the shock was omitted (extinction), and no tone or a tone of 250, 500, 1000, 2000, or 4000 Hz was presented following each press for the remainder of the session. Gradients of generalization plotted in terms of the number of times the tone was produced on each test peaked at 1000 Hz, indicating that the performance was controlled by the frequency. Since this dimension is orthogonal to absence of tone, the gradient cannot be attributed to differences in the magnitude of change in the warning signal. It was concluded that response-produced stimuli reinforce avoidance behavior.     

Liberating Behavior from Time-Bound Control: Expanding the Present Through Hypnosis1

Temporal perspective was experimentally manipulated by verbal instructions to expand the present while minimizing the significance of past and future. The reactions of trained hypnotic subjects to this induction were compared with hynotic simulators and nonsimulating controls. In a fourth group, time sense was made salient but no suggestion given to alter it. Across a variety of tasks, self-report measures, and behavioral observations, this modification of the boundaries between past, present, and future resulted in profound consequences among the hypnotic subjects. Changes in affect, language, thought processes, sensory awareness, and susceptibility to social-emotional contagion, accompanied an expanded present orientation. Nonreactive measures distinguished simulators from hypnotic subjects who apparently were better able than control subjects to incorporate the induced time distortion and perceive it as a viable alternative to their traditional time perspective. Some implications of time as a pervasive, non-obvious, independent variable in the social control of cognition and behavior are outlined.     

Repetition and practice effects in a lexical decision task

Ss classified visually presented verbal units into the categories “in your vocabulary” or “not in your vocabulary.” The primary concern of the experiment was to determine if making a prior decision on a given item affects the latency of a subsequent lexical decision for the same item. Words of both high and low frequency showed a systematic reduction in the latency of a lexical decision as a consequence of prior decisions (priming) but did not show any reduction due to nonspecific practice effects. Nonwords showed no priming effect but did show shorter latencies due to nonspecific practice. The results also indicated that many (at least 36) words can be in the primed state simultaneously and that the effect persists for at least 10 min. The general interpretation was that priming produces an alteration in the representation of a word in memory and can facilitate the terminal portion of the memory search process which is assumed to be random.     

Repetition effects in choice reaction time to multidimensional stimuli

Ss classified as quickly as possible stimuli back-projected one at a time on a small screen by pressing one of two levers in response to each stimulus, according to the levels of a single specified binary stimulus dimension. Stimuli were rectangles varying in height alone, in width alone, or in both dimensions, in either a correlated or an orthogonal fashion. Stimuli followed responses by a fixed interval of 82, 580, or 1,080 msec. Response time was longer when both dimensions varied orthogonally than when only one dimension varied, indicating that Ss were unable to avoid perceiving the rectangle figures as wholes. Repeated stimuli were responded to more quickly than stimuli which were different from the immediately preceding stimulus in all conditions. With orthogonally combined dimensions, response time to stimulus repetitions was lowest, increased when the stimulus changed while the response was repeated, and increased still further when both the stimulus and the response changed. Increasing the time interval between stimuli decreased response time for nonrepetitions, while response time for repetitions was relatively unaffected. The results were discussed in terms of two models of serial choice reaction time.