Gustav Theodor Fechner: life and work in the mirror of his diary

The diaries of Gustav Fechner reveal much about his motivations to develop the field of psychophysics, as well as some of the steps toward its formulation. Together with his publications on various subjects, the diaries show how psychophysics fits into Fechner's broader scientific program, illuminate his worldview, and reveal his hopes for acceptance of his work by his colleagues.     

Virtual reality and the new psychophysics

Virtual reality (VR) promises methodological rigour with the extra benefit of allowing us to study the context-dependent behaviour of individuals in their natural environment. Pan and Hamilton (2018, Br. J. Psychol.) provide a useful overview of methodological recommendations for using VR. Here, we highlight some other aspects of the use of VR. Our first argument is that VR can be useful by virtue of its differences from the normal perceptual environment. That is, by virtue of its relative non-realism and poverty of its perceptual elements, it can actually offer increased clarity with respect to the features of interest for the researcher. Our second argument is that VR exerts its measurable influence more by eliciting an acceptance of the virtual world (i.e., ‘suspension of disbelief’) rather than by eliciting a true belief of the realism of the VR environment. We conclude by providing a novel suggestion for combining neuroimaging methods with embodied VR that relies on the suspension of disbelief.     

On the preliminary psychophysics of fingerprint identification

For a century, the matching of images of fingerprints has been used for forensic identification. Despite that history, there have been no published, peer-reviewed studies directly examining the extent to which people can correctly match fingerprints to one another. The results of three experiments using naïve undergraduates to match images of fingerprints are reported. The results demonstrate that people can identify fingerprints quite well, and that matching accuracy can vary as a function of both source finger type and image similarity.     

The psychophysics of the pursuit oculomotor system

When a fixation point moves under a row of identical targets at a speed of one target for each flash of a strobe, smooth apparent movement of the targets is seen (the "picket-fence illusion"). When the fixation point is removed, the eye continues to pursue the apparent target movement. Pursuit continues through small changes in target configuration, but is interrupted by a change to a very dissimilar target (such as 1 vs. x) in the middle of a row. This new method, the "pursuit-interruption method," showed that large differences in the number of pixels in a line did not interrupt tracking if the end points of the line were preserved. Pursuit interruption by changes in line orientation (such as /vs./) corresponded to the orientation bandwidth of orientation-sensitive cortical neurons. The maximum number of consecutive missing targets that does not interrupt pursuit depends on frequency of target presentation as well as on parameters of the pursuit system.     

Stuck in the middle: the psychophysics of goal pursuit

The classic goal-gradient hypothesis posits that motivation to reach a goal increases monotonically with proximity to the desired end state. However, we argue that this is not always the case. In this article, we show that motivation to engage in goal-consistent behavior can be higher when people are either far from or close to the end state and lower when they are about halfway to the end state. We propose a psychophysical explanation for this tendency to get "stuck in the middle." Building on the assumption that motivation is influenced by the perceived marginal value of progress toward the goal, we show that the shape of the goal gradient varies depending on whether an individual monitors progress in terms of distance from the initial state or from the desired end state. Our psychophysical model of goal pursuit predicts a previously undiscovered nonmonotonic gradient, as well as two monotonic gradients.     

The psychophysics of retrospective and prospective timing

In two experiments, different groups of subjects heard four musical selections and then estimated the duration of each selection. Some groups made retrospective time estimates while others made prospective estimates. In both experiments, analyses of the psychophysical relation between perceived and actual duration showed that the slopes of straight-line fits were flatter and accounted for a smaller proportion of the variance under retrospective as compared with prospective conditions. In addition, in experiment 1, retrospective subjects were less accurate in rank ordering the selections from longest to shortest. There was also a serial-order effect, with selections estimated longer when they occurred early in the sequence. In experiment 2 the slopes decreased as the selections in a series became longer. Both retrospective and prospective estimates also exhibited a context effect, in that estimates of a given selection were influenced by the relative durations of the other three selections in the series. The results on inaccurate retrospective judgments raise questions about prior research on stimulus factors and retrospective timing. However, similarities under retrospective and prospective conditions suggest that timing under these conditions, although different in some respects, reflects a similar process.     

Counting and timing models in psychophysics and the conjoint Weber's law

J. C. Falmagne, G. Iverson, and S. Marcovici ((1979). Psychological Review, 86, 25–43) proposed a generalization of Weber's law, which they called the conjoint Weber's law. Empirically, the law sometimes holds. When it fails, the data satisfy a relation that Falmagne et al. identify as the conjoint Weber's inequality. This paper investigates the ability of counting and timing models of psychophysics to predict Weber's law and the conjoint Weber's law. It is shown that although the timing model naturally predicts both laws to hold, all reasonable counting models predict them to fail. Instead, counting models naturally predict Weber's inequality and the conjoint Weber's inequality.     

Significance of time scale differences in psychophysics

We present modeling of both rational processes (thoughts) and emotional processes (feelings) on a two-dimensional lattice and on extremely simplified two-dimensional phase space of the brain. Our purpose is to analyze influence of differences in time-scales of various types of processes. In particular, we show that no ‘central executive structure’ between consciousness and unconsciousness, the existence of which was suggested by psychologists, is not needed.     

Animal psychophysics: improvements in the tracking method.

It is difficult to maintain stimulus control in animal psychophysical studies using the tracking method. Loss of stimulus control is characterized by wandering thresholds and responses in the absence of the stimulus. Rats were trained to make a variable number of licking responses to turn on an auditory stimulus. A response on a lever in the presence of the stimulus was reinforced with food. Two precedures were added to improve stimulus control. First, lever responses in the absence of the stimulus raised the intensity of the stimulus at the next presentation; second, rate of reinforcement in the threshold region was maintained at about the same level as that in the suprathreshold region by reducing the number of licking responses required to turn on the stimulus. Using these two procedures, stimulus control was improved and maintained and reliable auditory intensity thresholds were obtained.     

Significance of time scale differences in psychophysics

We present modeling of both rational processes (thoughts) and emotional processes (feelings) on a two-dimensional lattice and on extremely simplified two-dimensional phase space of the brain. Our purpose is to analyze influence of differences in time-scales of various types of processes. In particular, we show that no ‘central executive structure’ between consciousness and unconsciousness, the existence of which was suggested by psychologists, is not needed.     

Additional rules for the transformed up-down method in psychophysics

In a classic paper, Levitt (1971) described an adaptive procedure for estimating points on the psychometric function known as thetransformed up-down method. Levitt discussed the assumptions of the method and presented a brief table with simple rules that converge to a few different points on the psychometric function. Levitt’s original table contains only the simplest rules, and sparsely covers the range of the psychometric function. This paper provides a table with previously unpublished rules which cover the range of the psychometric function at 5% intervals. There is a brief review of the major issues in adaptive testing. Technical issues such as the mean length and logical construction of the new rules are discussed.     

Evaluation of maximum-likelihood estimators in nonintensive auditory psychophysics

This is a brief report on the use of maximum-likelihood (ML) estimators in auditory psychophysics. Slope parameters of psychometric functions are characterized for three nonintensive auditory tasks: forced-choice discrimination of interaural time differences (ΔITD), frequency (Δf), and duration (Δt). Using these slope estimates, the ML method is implemented and threshold estimates are obtained for the three tasks and compared with previously published data. ΔITD thresholds were additionally measured for human observers by means of two other psychophysical procedures: the constant-stimuli (CS) and the 2-down 1-up methods (Wetherill & Levitt, 1965). Standard errors were smallest for the ML method. Finally, simulations showed ML estimates to be more efficient than the CS andk-down 1-up procedures fork=2 to 5. For up—down procedures, efficiency was highest fork values of 3 and 4. The entropy (Shannon, 1949) of ML estimates was the smallest of the simulated procedures, but poorer than ideal by 0.5 bits.     

The Euclidean model of measurement in Fechner's psychophysics

Historians acknowledge Euclid and Fechner, respectively, as the founders of classical geometry and classical psychophysics. At all times, their ideas have been reference points and have shared the same destiny of being criticized, corrected, and even radically rejected, in their theoretical and methodological aspects and in their epistemological value. According to a model of measurement of magnitudes which goes back to Euclid, Fechner (1860) developed a theory for psychical magnitudes that opened a lively debate among numerous scholars. Fechner's attempt to apply the model proposed by Euclid to subjective sensation magnitudes--and the debate that followed--generated ideas and concepts that were destined to have rich developments in the psychological and (more generally) scientific field of the twentieth century and that still animate current psychophysics.     

The psychophysics of the kinesthetic aftereffect in the Petrie block experiment

Kinesthetic size is reported in the Petrie experiment by a simultaneous size comparison in which a standard block held between the thumb and forefinger of one hand is matched in size by moving the thumb and forefinger of the opposite hand along a wedge until the proper width is reached. After a baseline is obtained, a kinesthetic aftereffect is produced by rubbing a block of contrasting size followed by a return to the standard block. Experiments with 22 male Ss and 20 female Ss, tested in separate cycles, show that augmentation following stimulation with a block smaller than standard and reduction following stimulation with a block larger than standard are both statistically significant, and, at least for augmentation, the aftereffect persists for at least 48 h. When the data are corrected for regression there is no significant relationship between initial baseline and the amount of augmentation or reduction; reasons why such a relationship has been reported are indicated. The results suggest that when this kind of experiment is used for the study of individual differences (a) it is satisfactory to derive augmentation and reduction scores by subtracting the baseline from the absolute scores, provided the scores are corrected for regression, and (b) a counterbalanced order of presentation is not advisable in view of the carryover of augmentation from one day to the next, which is likely to make the two orders incommensurate.     

Limulus psychophysics: dark adaptation in the ventral eye.

Sudden illumination applied to Limulus produces an unconditioned downward tail movement which is under stimulus control and can be used to measure psychophysical thresholds. The method of constant stimuli was used to measure the behavioral dark-adaptation function mediated by the ventral eye of Limulus. The resulting function has two phases, each of which is rectified when log threshold is made a function of long time in the dark. Under the conditions of the present experiment, the transition between the two phases occurred at 6 min. This psychophysical dark-adaptation function has the same form as an electrophysiologic dark-adaptation function obtained by Fein and DeVoe (using the ventral eye receptor potential as the response). In more complex visual systems such two-phase, dark-adaptation functions would usually be interpreted in terms of screening pigment movements or changes in the neural contributions of different receptor classes, but neither interpretation is appropriate for the ventral eye of Limulus.