Non-random sequences in visual threshold experiments

Responses (i.e. “seen” or “not seen”) to a repeated stimulus of constant intensity are shown to be grouped in runs of the same response. It is suggested that there are only two possible explanations of this non-randomness: spontaneous fluctuations of threshold and the direct influence of a response on succeeding responses. Experiments designed to distinguish between these two explanations have shown that the latter is the more important and that a response affects directly, though with diminishing intensity, the three immediately following responses.     

Outline forms as visual stimuli in psychological experiments

Summary A set of stimuli to be used in psychological experiments is presented. Drawn spontaneously by the Ss, these stimuli are outline forms which can be freely reproduced in an experimental situation. The complexity and meaning-fulness of 100 forms were investigated. Meaningfulness depended on two variables: the probability of a given form having a certain meaning for a S, and the homogeneity of the meanings a given number of Ss ascribe to this form. Three types of meaningfulness could be distinguished: forms with one meaning only, ambiguous forms and nonsense forms. Complexity, homogeneity and probability of having a meaning are listed for all 100 forms.This research was carried out as part of a doctoral dissertation at the Department of Behavior Science of the Swiss Federal Institute of Technology in Zurich. The author expresses gratitude firstly to his supervisors, Professor H. Fischer and Professor K. Bättig, for their encouragement and criticism throughout the research. Thanks are also due to Professor Klaczko and Dr. H.U. Baumann for their many valuable suggestions, to Laurel Gutmann, Professor A. Flammer and Professor M. Perrez for their many helpful comments on earlier drafts of the paper, and to W.G. Hoffmann and R. Casetti for their further assistance.     

A multiprocessor system for generating visual displays and controlling experiments

A laboratory is described that is based on an IMSAI 8080 microcomputer and an IMLAC graphics display system. Procedures for using the system are described and illustrated.     

VSearch: Macintosh software for experiments in visual search

In this paper, we describe software that turns a Macintosh computer into an off-the-shelf tool for experiments on visual search. Our design goals included portability (between members of the Macintosh computer family and between various research settings), user-friendliness (equivalent to Macintosh programming standards), flexibility (to allow replication and extension of important experiments on visual search), and adaptability (very short design-to-data and data-to-analysis turnaround times). We describe how the software meets these goals in three major phases of an experiment: stimulus construction, experimental control, and statistical analysis. We then list several landmark studies of visual search that can be easily designed and extended with the software. Finally, we outline plans for expanding the experimental variations that will be supported in future versions of the software.     

VSearch Color: Full-color visual search experiments on the Macintosh II

We describe an update to our visual search software for the Macintosh line of computers. The new software, VSearch Color, gives users access to the full-color capabilites of the Macintosh II line. One of the key features of the new software is its ability to treat graphics information separately from color information. This makes it easy to study color independently of form, to design experiments based on isoluminant stimuli, and to incorporate texture segregation, visual identification, number discrimination, adaptation, masking, and spatial cuing into the basic visual search paradigm.     

The eyes have it: Exposure times and saccadic movements in visual half-field experiments

Several tachistoscopic visual half-field experiments using exposure times in excess of 150 msec have been reported and arguments have been put forth justifying this procedure. An experiment was done investigating visual field accuracy under conditions where eye movement was allowed, following parafoveal exposure. Two control experiments were done to evaluate the viewing conditions. When eye movement is permitted, accuracy in both visual fields reaches 100%. It is concluded that visual field differences found with exposure times greater than 150 msec are due to the active cooperation of the subjects and not due to the justifications advanced by experimenters using long exposure times.     

Magnifying effects on visual word recognition: a dynamic display for internet-based experiments

A visual presentation procedure is introduced that presents target words followed by a dynamic mask until recognition. This form of stimulus degradation prolongs the word recognition process. Differences in word recognition latencies—which are usually quite small—are magnified, and thus can be more easily observed. The results of two experiments on the Internet with a total of 141 participants establish the task’s ability to magnify differences in word recognition latencies stemming from word familiarity (Experiment 1) and word prototypicality (Experiment 2). Both factors interact with stimulus degradation, but at different presentation intervals; these results are discussed as evidence for comparing models of word recognition. The new procedure can be used for assessing individual differences, such as implicit motives and self-focused attention. Further applications are discussed.     

The photoneuromime: An artificial visual neuron for dynamic testing of computer-controlled experiments

The photoneuromime is a simple electronic device that produces frequency-modulated pulses resembling neural spike trains in response to light modulation. It simulates the linear behavior of cat retinal ganglion X-cell receptive field centers and was designed for testing computer programs that track sensitivity to patterns generated on a raster-scan CRT. Besides providing a convenient means for testing computer programs and recording apparatus, which previously required the use of a live preparation, the neuromime is also a valuable teaching tool in sensory psychology and neuroscience.     

A random-walk model of accuracy and reaction time applied to three experiments on pigeon visual discrimination

A random-walk model of visual discrimination is described and applied to reaction time (RT) distributions from three discrete-trial experiments with pigeons. Experiment 1 was a two-choice hue discrimination task with multiple hues. Choice percentages changed with hue discriminability; RTs were shortest for the least and most discriminable stimuli. Experiments 2 and 3 used go/no-go hue discriminations. Blocks of sessions differed in reward probability associated with a variable red stimulus in Experiment 2 and with a constant green stimulus in Experiment 3. Changes in hue had a large effect on response percentage and a small effect on RT; changes in reward shifted RT distributions on the time axis. The "random-walk, pigeon" model applied to these data is closely related to Ratcliff's diffusion model (Ratcliff, 1978; Ratcliff & Rouder, 1998). Simulations showed that stimulus discriminability affected the speed with which evidence accumulated toward a response threshold, in line with comparable effects in human subjects. Reward probability affected bias, modeled as the amount of evidence needed to reach one threshold rather than the other. The effects of reward probability are novel, and their isolation from stimulus effects within the decision process can guide development of a broader model of discrimination.     

The PEPL system for control of experiments by a PDP-8 computer

PEPL (Psychology Experiment Programming Language) is a real-time, on-line experimental control system designed for a 4K PDP-8 computer with minimal additional hardware. The system, consisting of the PEPL language, a symbol table for standard DEC assemblers, and an operating system, is capable of asynchronous, timed control of multiple subjects or experiments. The language offers the user high-level instructions for execution control, computation, timing, and I/O control.     

Effect of grammatical gender on visual word recognition: evidence from lexical decision and eye movement experiments

Lexical decision times and eye movements were recorded to determine whether grammatical gender can influence the visual recognition of isolated French nouns. This issue was investigated by assessing the use of two types of regularities between a noun's form and its gender--namely ending-to-gender regularities (e.g., the final letter sequence -at appears only in masculine nouns and, thus, is predictive of masculine gender) and gender-to-ending regularities (e.g., feminine gender would predict the final letter e, whereas masculine gender would not). Previous studies have shown that noun endings are used by readers when they have to identify gender. However, the influence of ending-to-gender predictiveness has never been investigated in a lexical decision task, and the effect of gender-to-ending regularities has never been evaluated at all. The results suggest that gender information can influence both the activation stage (Experiments 1 and 3) and the selection stage (Experiments 2 and 3) of the word recognition process.     

Using facial emotional stimuli in visual search experiments: The arousal factor explains contradictory results

For more than two decades, visual search experiments using pictures of emotional faces as stimuli have generated contradictory results. Evidence of a superior detection of angry faces compared to happy faces have been mixed with an equal amount of evidence in the opposite direction. In this article, we review this literature, and examine the hypothesis that the neglected stimulus factor of emotional arousal may explain these contradictory results. Through an extensive reanalysis of results from our own laboratory as well as from other researchers, we show that the arousal factor systematically influences the outcome of the reviewed visual search experiments, and may thus provide a key to the historical contradictions within this research field.