Task-performance of spinal-cord injured individuals as a function of level of motivational demand
The purpose of this exploratory study was to determine if spinal-cord injured and normal individuals differ in task-performance under various degrees of motivational demand. Traditionally, two main approaches to conceptualizing the behavioral effects of severe spinal-cord injury have been: 1) to view spinal-cord injured individuals as simply representative of disabled persons, or 2) to focus upon the specific sensory and motor deficits which limit the individual's performance capabilities. The present study stemmed from the alternative viewpoint that: 1) severe spinal-cord injury may have pervasive effects upon the individual's motivational and affective functioning; 2) these effects are specifically attributable to the reduction of afferent stimulation from proprioceptive and cutaneous sources to the activation system. Twenty spinal-cord injured male patients (median age = 22. 5) who had all sustained functionally complete spinal-cord lesions resulting in complete loss of motor and sensory functioning below the level of lesion and twenty normal male Ss (median age = 19. 5) performed a verbal serial-coding task for 3-min. periods under each of three levels of motivational demand-- low, moderate, and high. A low level of motivational demand consisted of telling the Ss that their performance was for practice purposes (Practice Condition). The moderate and high levels of motivational demand were achieved by telling the Ss that their performance would be scored and "count" (Score-Count Condition) and by offering the Ss monetary reward (Money-Reward Condition) for improved performance. Two separate performance indices were assessed -- the number of errors and the number of items completed. An attempt was made to assess independently the efficacy of the three levels of motivational demand by electromyographically recording integrated muscle potentials from the forehead and neck muscles. An effort was also made in the present study to determine if spinal-cord injured patients and normals would differ in performing a markedly different type of task (viz., simple reaction time) which consisted of having the Ss respond by raising their eyebrows to the offset of a light under a single, relatively high level of motivational demand. The results of the study revealed that the profound neurological deficit and consequently disrupted physiological functioning resulting from functional transection of the spinal cord does not substantially alter the individual's cognitive functioning under varied motivational conditions or the speed of his motor responses. For the Verbal-Coding Task, there were no differences between the normal and spinal-cord injured Ss in the number of errors committed and in the total number of items completed. The number of items completed by each group was similarly affected by the three motivational conditions in the intended manner. Reliable differences were obtained, however, between the two groups for the number of items attempted in specific 30-sec. intervals of this task. Specifically, the normals attempted significantly more items during- the first and fifth 30-sec. intervals irrespective of the motivational conditions. At best, this provides marginal support for the original supposition underlying this study that task-performance differences exist between normals and spinal-cord injured patients. This time-dependent difference in the performance of the two groups may be based upon the ability of the normals to mobilize initially higher activation levels which facilitates their performance. In the absence of substantial task-performance differences between the two groups, however, it was conjectured that powerful sources for task-facilitating activation, such as arising from the face and cortex, must remain intact for the spinal-cord injured patients. The EMG data revealed that both muscles manifested changes, though not always reliable ones, in EMG activity between the various experimental periods. Both muscles displayed increased EMG activity during taskperformance conditions and lessened EMG activity during periods of rest and quiescence. The frontalis muscle appeared to be insensitive for reflecting variations in motivational demand, but closely paralleled the gradual decline in the number of items completed during any given trial of the Verbal-Coding Task. This latter finding may reflect adaptation of the frontalis to decreasing vocalization and eye-movements. In contrast, the EMG activity of the trapezius displayed increased activity during task-performance and was more sensitive to variations in motivational demand. Higher trapezius EMG activity, even during periods of rest, among the spinal-cord injured Ss, however, appeared to reflect the importance of this muscle in the maintaining balance and posture. The bulk of the EMG results thus showed that both muscles displayed a specificity of response which precludes any confident interpretive statements regarding the Ss' psychological state under the various conditions of the experiment.