The effect of stimulation waveform on pattern perception was investigated on a 49-point fingertip-scanned electrotactile (electrocutaneous) display. Waveform variables burst frequency (F), number of pulses per burst (NPB), and pulse repetition rate (PRR) were varied in a factorial design. Contrast reduction was used to limit performance of perceiving a 1-tactor gap defined within a 3 x 3 tactor outline square. All three variables accounted for significant variations in performance with higher levels of F and NPB and lower levels of PRR, leading to better performance. In addition, we collected qualitative data on each waveform, and the qualitative differences were related to performance (e.g., waveforms perceived as having a more localized sensation were correlated with better pattern identification performance than those waveforms perceived as more broad). We also investigated the effect of stimulation contrast on pattern perception.

Electrovibration is tactile sensation of an alternating potential between the human body and a smooth conducing surface when the skin slides over the surface and where the current is too small to stimulate sensory nerves directly. It has been proposed as a high-density tactile display method, for example to display pictographic information to persons who are blind. Previous models for the electrovibration transduction mechanism are based on a parallel-plate capacitor, in which the electrostatic force is insensitive to polarity. We present experimental data showing that electrovibratory perceptual sensitivity to positive pulses is less than that for negative or biphasic pulses, and propose that this disparity may be due to the asymmetric electrical properties of human skin. We furthermore propose using negative pulses for insulated tactile displays based on electrovibration because their sensory thresholds were found to be more stable than for waveforms incorporating positive pulses.

The present experiments extend the scope of the independent observation model based on signal detection theory (Macmillan & Creelman, 1991) to complex (word) stimulus sets. In the first experiment, the model predicts the relationship between uncertain detection and subsequent correct identification, thereby providing an alternative interpretation to a phenomenon often described as unconscious perception. Our second experiment used an exclusion task (Jacoby, Toth, & Yonelinas, 1993), which, according to theories of unconscious perception, should show qualitative differences in performance based on stimulus detection accuracy and provide a relative measure of conscious versus unconscious influences (Merikle, Joordens, & Stoltz, 1995). Exclusion performance was also explained by the model, suggesting that undetected words did not unconsciously influence identification responses.

The independent observation model (Macmillan& Creelman, 1991)is fitted to detection-identification data collected under conditions of heavy masking. The model accurately predicts a quantitative relationship between stimulus detection and stimulus identification over a wide range of detection performance. This model can also be used to offer a signal detection interpretation of the common finding of above-chance identification following a missed signal. While our finding is not a new one, the stimuli used in this experiment (redundant three-letter strings) differ slightly from those used in traditional signal detection work. Also, the stimuli were presented very briefly and heavily masked, conditions typical in the study of unconscious perception effects.

A common strategy in unconscious perception research is to use either pattern masking or metacontrast masking to render prime stimuli “invisible” to consciousness. However, several recent studies have questioned whether the identities of prime stimuli (typically arrows or diamonds and squares) in metacontrast masking studies are impossible to consciously perceive. In a series of studies, we concurrently related prime awareness, target response time priming, and prime identification across 3 prime–mask stimulus onset asynchronies (27, 40, and 67 ms). We found that increases in prime awareness ratings were accompanied by better prime identification performance. Significant prime identification in the 27-ms condition was obtained only at the highest awareness rating; for the other 2 stimulus onset asynchronies most awareness ratings were associated with above-chance prime identification. The priming effects obtained in these paradigms occur, to some degree, when participants are likely to be aware of the prime stimuli. Our results, collectively, suggest that metacontrast masking of primes does not necessarily preclude their awareness. Priming effects may depend on at least partial awareness of the prime stimuli.