Shawn Stafford

The Effects of Physiological Stress on Tactile Communication

The researcher-constructed tactile display prototype has been used to conduct a variety of laboratory studies that have demonstrated positive results for tactile signaling and communication. This prototype display that uses precision tactors and skilled placement of them exhibits potential for superior reception of the vibration in the appropriate skin receptors. The purpose of this study was to determine if this prototype tactile display could still produce accurate reception of tactile localization and messaging under physiological stress. Results showed that USMA cadets running on a treadmill had almost error free performance, demonstrating that messaging and localization of tactile signals seemed to be unaffected by physiological arousal or stress.

The Workload and Performance Relationship in the Real World: A Study of Police Officers in a Field Shooting Exercise

We examined the relationship between perceived workload and performance by evaluating the responses of police officers to 4 different draw-and-shoot tasks in a night field training exercise which was part of their regular training regimen. Sixty-two police officers volunteered to participate. Results demonstrated an associative trend among 3 tasks where shooting performance decreased and workload increased as the tasks became more complex. However, performance on 1 specific shooting task did not correlate with any of the other 3 tasks, and in this 1 exceptional case, insensitivities were observed in which workload increased but performance remained constant.

The effects of display size on performance

We examined the systematic effects of display size on task performance as derived from a standard perceptual and cognitive test battery. Specifically, three experiments examined the influence of varying viewing conditions on response speed, response accuracy and subjective workload at four differing screen sizes under three different levels of time pressure. Results indicated a ubiquitous effect for time pressure on all facets of response while display size effects were contingent upon the nature of the viewing condition. Thus, performance decrement and workload elevation were evident only with the smallest display size under the two most restrictive levels of time pressure. This outcome generates a lower boundary threshold for display screen size for this order of task demand. Extrapolations to the design and implementation of all display sizes and forms of cognitive and psychomotor demand are considered. Practitioner Summary: This work specifies the effect of display size on operator performance. It presents a threshold for an acceptable level of response time and accuracy contingent upon time pressure imposed and display size presented. The procedure provides vital information for all future designers and users of displays.

A Wireless Tactile Communication System for Conveying U.S. Army Hand-Arm Signals

Combat conditions place fearsome extremes on soldier senses, rendering many traditional visual and auditory informational pathways unusable for soldier communications. To circumvent these limitations, vibrotactile displays may offer environmental advantages (covert use in murky and noisy conditions) as well as human information processing advantages (an unimpeded sensory channel and potential resource pool). The demonstrated system uses wireless electronic communications to present exemplar Army arm and hand signals in a tactual form. Vibrotactors on an elasticized belt deliver vibrotactile patterns to the wearers torso, with inputs originating from a hardened PDA running a custom software package. Benefits and limitations are discussed, as well as other potential applications and integrations with other information input sources.

Workload and Performance: A Field Evaluation in a Police Shooting Range

One vital responsibility of all law enforcement officers lies in their obligation to defend themselves and those around them in the event of a violent threat. The best tool available to them to perform this duty is their sidearm and their skill in using it. To evaluate the efficiency of this tool use, seventy-one police officers participated in a field study examining the relationship between workload and shooting performance. Use of linear regression analysis produced evidence linking higher reported workload on the mental subscale of the NASA-TLX while completing a shooting task to poorer shooting performance when controlling for marksmanship skill. This finding is discussed in the context of previous work in the areas of workload and attentional allocation.

Application of Fuzzy Signal Detection Theory to Vigilance: The Effect of Criterion Shifts

A recent advance on Signal Detection Theory (SDT) promises to enhance measurement of performance in complex real world domains. This development, Fuzzy Signal Detection Theory (FSDT), combines traditional SDT with Fuzzy Set Theory to extend signal detection analysis beyond the traditional crisp, categorical model. FSDT permits events to simultaneously be in more than one state category (e.g. signal and non-signal), so that the stimulus and response dimensions can be continuous rather than categorical. Consequently, FSDT can be employed in settings where the degree to which an event is a signal for detection may vary. This study is an initial test of application of FSDT to vigilance, a domain in which SDT has been widely applied. Results indicate that manipulations of stimulus probability impacts response bias in a fuzzy vigilance task, but that these effects differ somewhat from tasks employing traditional signal detection.

Individual Differences Related to Shooting Performance, in a Police Night-Training Shooting Exercise

Increased understanding of the stress and performance effects of gun range drills with police officers is of importance for law enforcement trainers. Seventy-one police officers participated in routine night shooting drills over a two week period as part of regular training regimen. This paper examines the effects of two shooting range tasks on police officers time perception, individual differences, and shooting performance. Theoretical considerations led to the hypothesis that performance changes under stress may be related to distortions in the perception of time. However, the results of this study do not provide strong evidence for nomothetic effects of time distortion. Rather, it is more likely a function of individual differences. Future studies will examine potential individual differences variables that influence the relation between time distortion under stress and task performance.