Christian Kaernbach

Simple adaptive testing with the weighted up-down method

This paper proposes a method for adaptive testing that is less complicated than the commonly used transformed up-down methods (1 up 2 down, 1 up 3 down, etc.). In addition, the weighted up-down method can converge to any desired point of the psychometric function. The rule is very simple: Each correct response leads to a decrease in signal level, each incorrect response to an increase. The only difference from the simple up-down method (1 up 1 down) is that the steps upward and the steps downward are of a different size. The straightforward construction of the novel procedure pays off in efficiency and stability: A Monte Carlo simulation reveals a definite advantage, though small, of the weighted up-down method over the 1-up-2-down rule.

A continuous measure of phasic electrodermal activity

Electrodermal activity is characterized by the superposition of what appear to be single distinct skin conductance responses (SCRs). Classic trough-to-peak analysis of these responses is impeded by their apparent superposition. A deconvolution approach is proposed, which separates SC data into continuous signals of tonic and phasic activity. The resulting phasic activity shows a zero baseline, and overlapping SCRs are represented by predominantly distinct, compact impulses showing an average duration of less than 2 s. A time integration of the continuous measure of phasic activity is proposed as a straightforward indicator of event-related sympathetic activity. The quality and benefit of the proposed measure is demonstrated in an experiment with short interstimulus intervals as well as by means of a simulation study. The advances compared to previous decomposition methods are discussed.

Decomposition of skin conductance data by means of nonnegative deconvolution

Skin conductance (SC) data are usually characterized by a sequence of overlapping phasic skin conductance responses (SCRs) overlying a tonic component. The variability of SCR shapes hereby complicates the proper decomposition of SC data. A method is proposed for full decomposition of SC data into tonic and phasic components. A two-compartment diffusion model was found to adequately describe a standard SCR shape based on the process of sweat diffusion. Nonnegative deconvolution is used to decompose SC data into discrete compact responses and at the same time assess deviations from the standard SCR shape, which could be ascribed to the additional process of pore opening. Based on the result of single non-overlapped SCRs, response parameters can be estimated precisely as shown in a paradigm with varying inter-stimulus intervals.

Adaptive threshold estimation with unforced-choice tasks.

This paper evaluates an adaptive staircase procedure for threshold estimation that is suitable for unforced-choice tasks—ones with the additional response alternativedon’t know. Within the framework of a theory of indecision, evidence is developed that fluctuations of the response criterion are much less detrimental to unforced-choice tasks than to yes/no tasks. An adaptive staircase procedure for unforced-choice tasks is presented. Computer simulations show a slight gain in efficiency ifdon’t know responses are allowed, even if response criteria vary. A behavioral comparison with forcedchoice and yes/no procedures shows that the new procedure outdoes the other two with respect to reliability. This is especially true for naive participants. For well-trained participants it is also slightly more efficient than the forced-choice procedure, and it produces a smaller systematic error than the yes/no procedure. Moreover, informal observations suggest that participants are more comfortable with unforced tasks than with forced ones.

A single‐interval adjustment‐matrix (SIAM) procedure for unbiased adaptive testing

A new unbiased adaptive procedure is described that requires only half as many presentations in achieving the same precision as the well-known two-interval forced-choice (2IFC) 2-step procedure. The procedure is based on a yes-no task which avoids redundant presentation time. Furthermore, certain psychophysical studies can only be realized with yes-no tasks. Every trial contains randomly presented signals or noises and the answer is either yes or no. The outcome (hit, miss, false alarm, correct rejection) is taken into account by adjusting the signal level in a staircase manner. The adjustment matrix is set up to induce a neutral response criterion. Its convergence point can be adjusted at will. The single-interval adjustment-matrix (SIAM) procedure is compared to von Békésy and 2IFC transformed up-down methods using a Monte-Carlo simulation. The SIAM procedure proves to be the fastest of the unbiased procedures. A test on four subjects verified these results. Implications for optimum track length and the number of reversals to discard are discussed.

Physiological correlates and emotional specificity of human piloerection.

Research highlights ► Film audio tracks are more powerful than music in eliciting piloerection. ► Objective measurement of piloerection avoids typical biases of self-report measures. ► Piloerection is primarily accompanied by an increase of phasic EDA and respiration depth. ► The separation call hypothesis is favored over the peak arousal hypothesis. ► Emotional piloerection indicates the state of being moved or touched.

Exploring the temporal mechanism involved in the pitch of unresolved harmonics

This paper continues a line of research initiated by Kaernbach and Demany [J. Acoust. Soc. Am. 104, 2298-2306 (1998)], who employed filtered click sequences to explore the temporal mechanism involved in the pitch of unresolved harmonics. In a first experiment, the just noticeable difference (jnd) for the fundamental frequency (F0) of high-pass filtered and low-pass masked click trains was measured, with F0 (100 to 250 Hz) and the cut frequency (0.5 to 6 kHz) being varied orthogonally. The data confirm the result of Houtsma and Smurzynski [J. Acoust. Soc. Am. 87, 304-310 (1990)] that a pitch mechanism working on the temporal structure of the signal is responsible for analyzing frequencies higher than ten times the fundamental. Using high-pass filtered click trains, however, the jnd for the temporal analysis is at 1.2% as compared to 2%-3% found in studies using band-pass filtered stimuli. Two further experiments provide evidence that the pitch of this stimulus can convey musical information. A fourth experiment replicates the finding of Kaernbach and Demany on first- and second-order regularities with a cut frequency of 2 kHz and extends the paradigm to binaural aperiodic click sequences. The result suggests that listeners can detect first-order temporal regularities in monaural click streams as well as in binaurally fused click streams.

Effects of consciousness on human brain waves following binocular rivalry

When the two eyes of an observer are exposed to conflicting stimuli, they enter into binocular rivalry and the two possible percepts will alternate in dominance. We investigated neural activity and its time course following binocular rivalry by measuring human event-related brain potentials to transitions from rivalrous to non-rivalrous stimulation. When these changes did not entail a change in conscious perception they elicited a markedly attenuated N1 component and a delayed and attenuated P3 peak as compared to percept-incompatible changes and non-rivalrous control conditions. These results suggest that in humans binocular rivalry is resolved at latest in extrastriate visual areas.

Slope bias of psychometric functions derived from adaptive data.

Several investigators have fit psychometric functions to data from adaptive procedures for threshold estimation. Although the threshold estimates are in general quite correct, one encounters a slope bias that has not been explained up to now. The present paper demonstrates slope bias for parametric and nonparametric maximum-likelihood fits and for Spearman-Kärber analysis of adaptive data. The examples include staircase and stochastic approximation procedures. The paper then presents an explanation of slope bias based on serial data dependency in adaptive procedures. Data dependency is first illustrated with simple two-trial examples and then extended to realistic adaptive procedures. Finally, the paper presents an adaptive staircase procedure designed to measure threshold and slope directly. In contrast to classical adaptive threshold-only procedures, this procedure varies both a threshold and a spread parameter in response to double trials.

The Memory of Noise

The memory of auditory random waveforms (i.e., noise) is a special case of auditory memory for sensory information. Five experiments are reported that evaluate the dynamics of this storage system as well as interactions with new input. Periodic waveforms can be discriminated from uncorrelated noise by naive listeners up to a cycle length of 20 s, with the major decline in performance between 5 and 10 s. Even single repetitions of a piece of the waveform can be detected up to a stimulus onset asynchrony (SOA) of 6 s. The capacity of this storage system is limited to a few items of, in total, a few hundred milliseconds length. Within this capacity, however, items do not interfere strongly. These results are compatible with the view that auditory sensory memory is a modality-specific module of short-term memory.