Further experiments on probability-matching in the pigeon

In a discrete-trials, two-key choice situation, probability-learning by pigeons was studied under a variety of training conditions. Matching was found in simultaneous and in successive problems, but a spatial problem produced only maximizing. In the simultaneous problem, noncorrection produced maximizing, while correction produced matching. Guidance produced maximizing when the animals were required to earn each opportunity for choice by pecking a center key on FR-5, but matching when the center key was not used. In a discrete-trials one-key situation, with latency as the measure, frequency and probability of reinforcement were varied independently. Differences in probability produced differences in latency of response, but differences in frequency did not.     

Backward and forward masking associated with saccadic eye movement

Visual masking effects on test flash thresholds were measured under real and simulated eye movement conditions to determine whether visual masking is primarily responsible for elevations in threshold that are sometimes associated with saccadic eye movements. Brief luminous flashes presented to the central retina before, during, and after saccades were masked by stimuli presented either pre- or postsaccadically. The amount and time course of masking were quantitatively dependent on stimulus parameters of intensity and temporal separation and were unaffected by eye movement parameters (amplitude, velocity, direction) as long as retinal stimulus conditions were constant. The duration of forward masking was longer than that of backward masking. When retinal conditions during saccades were mimicked while the eyes were held steady, masking interactions were identical to those obtained during real saccades. These results indicate that masking effects during saccades in ordinary environments are determined solely by the stimulus situation at the retina. Putative nonvisual, centrally originating saccadic suppression suggested by other authors is evidently not additive with visually determined masking during saccades.     

Absence of masking in the path of apparent movement

Alternation of diagonal pairs of lights produced apparent movement which S could organize in either of two distinctly different ways, as instructed. The task was to detect movement of a weak probe light that either was or was not located in the path of the apparent movement, depending on the organization, stimulation being identical in the two cases. Results showed no evidence of path-specific masking.     

Further experiments on the perception of growth in three dimensions

Mark and Todd (1983) reported an experiment in which the cardioidal strain transformation was extended to three dimensions and applied to a three-dimensional (3-D) representation of the head of a 15-year-old girl in a direction that made the transformed head appear younger to the vast majority of their subjects. The experiments reported here extend this research in order to examine whether subjects are indeed detecting cardioidal strain in three dimensions, rather than detecting changes in head slant or making 2-D comparisons of the shape of the occluding contour. Three-dimensional surfaces were obtained by measuring a real head manually (Experiment 1) and with a laser scanner (Experiment 2), and transformed to different age levels using the 3-D strain transformation described by Mark and Todd (1983). There were no statistically significant differences in the accuracy with which relative age judgments could be made in response to pairs of profiles, pairs of 3/4 views, or pairs of mixed views (profile plus 3/4 view), suggesting that subjects can indeed extract the cardioidal strain level of the head in three dimensions. However, an additional effect that emerged in these studies was that judgments were crucially affected by the instructions given to subjects, which suggests that factors other than cardioidal strain are important in making judgments about rich data structures.     

Temporal masking level differences for transients: Further evidence for a short-term integrator

Studies of binaural perception have indicated that subjects are able to use temporal information available in high-frequency regions of the spectrum to lateralize high-frequency waveforms but not to detect these waveforms in masking noise. The present experiments demonstrate that although high-frequency interaural difference cues are relatively ineffective in simultaneous and forward masking, they can be utilized in backward masking. In Experiment 1, large maskinglevel differences were found in backward masking for high-frequency transients presented either monaurally or with an interaural temporal delay. Experiments 2–4 examined fringe masking, effects of masker duration, and combined forward-backward masking for both high- and lowfrequency transients presented with interaural differences in phase and intensity. The results are interpreted as support for the view that the auditory system is organized into parallel shortand long-term integration systems specialized for processing transient and sustained aspects of acoustic stimulation. It is suggested that information from the two integrators is combined when analysis of interaural differences within each of the systems yields similar estimates of spatial location.     

Crossed-uncrossed difference (CUD) on reaction time and movement time in three two-choice experiments

The present study addresses the robustness and the reliability of the crossed-uncrossed difference (CUD) on a reaction time (RT) and a movement time (MT) component of a prescribed unimanual response to lateralized stimuli. Experiment 1 demonstrated positive CUDs both when a visual warning signal (WS) and an auditory reaction signal (RS) appeared on corresponding and non-corresponding sides of the body. Experiment 2 showed effect of handedness on CUD calculated among right-handers and left-handers. Experiment 3 investigated CUDs through five successive days, indicating that CUDs became steady and reliable although practice affected both RT and MT. All experiments indicated CUD on RT and MT. In addition, Experiments 1 and 2 demonstrated hemispheric asymmetries in favour of an anatomical theory while Experiment 3 did not show any asymmetries and supports an S-R compatibility theory.     

Further experiments on the social interactions of domestic “Norway” rats

Domestic rats, Rattus norvegicus, aged nearly one year, were studied in artificial colonies in large cages with attached nest boxes. As in previous experiments on younger domestic rats, but not those on wild rats, the colonies were peaceful. Questions concerning the “aggressive” or “agonistic” behavior of domestic rats are further discussed.     

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.     

Interhemispheric visual masking

Backward masking functions were evaluated in a paradigm in which target and masking stimuli were presented to opposite cerebral hemispheres using separate peripheral pathways. Backward masking occurred dichoptically when the target and mask were projected to opposite hemispheres. These findings indicated that some effective masking mechanisms are mediated by interhemispheric interactions independent of retinal phenomena.     

Frequency selectivity using tonal-temporal masking: Diotic vs. dichotic masking

A combined forward-backward masking procedure was used to investigate the threshold of a 30-msec, 500-Hz signal as a function of masker frequency. The signal thresholds were obtained in two signal conditions, diotic (So) and dichotic (S_π), and for two different temporal separations of the maskers. The maskers were 500 msec in duration and were presented at 75 dB SPL. The function relating masked signal threshold to masker frequency was used to describe frequency selectivity in the four conditions. There were no differences in frequency selectivity measured between the diotic and dichotic signal conditions and only a small difference measured between the two intermasker interval conditions. The S_π conditions yielded lower thresholds than did the So conditions. The change in intermasker interval from 10 to 50 msec lowered the threshold maximally 18 dB for the So condition and 13 dB for the S_π condition. The results indicate that in this tonal temporal masking procedure there are no differences between the diotic and dichotic critical bands.     

Influence of temporal masking on click-pair discriminability

When temporal auditory acuity is estimated using time-reversed click pairs, the asymmetry of temporal masking may influence the results. To investigate this hypothesis, we first established normal-hearing listeners’ psychometric functions for the discrimination of time-reversed click pairs. An attempt to relate listeners’ performances in click-pair discrimination to their performances in forward and backward masking tasks was unsuccessful, probably due to the presence of spectral artifact in the temporal masking paradigms. We then investigated listeners’ abilities to discriminate time-reversed click pairs in which the intensity of the lower level click in one pair was altered. This alteration was introduced at random in order to minimize the influence of spectral artifact. Our results suggest that the course of temporal masking influenced the discriminability of the modified click pairs. Thus, the discrimination of time-reversed click pairs may yield a biased estimate of auditory temporal acuity.     

Perceptual learning in monocular pattern masking: experiments and explanations by the twin summation gain control model of contrast processing

We investigated practice effects on contrast thresholds for target patterns. Results showed that practice decreased contrast thresholds when targets were presented on maskers. Thresholds tended to decrease more at the higher end of the masker contrast range. At least partially, learning transferred to stimuli of the untrained phase. We simulated changes in threshold versus contrast functions using a contrast-processing model and then fit the model to pre- and posttraining data. The simulation results and model fit suggest that learning in pattern masking can be accounted for by changes in nonlinear transducer functions for divisive inhibitory signals.     

Transient and sustained masking

The detection threshold of a brief test stimulus was measured as a function of the onset asynchrony between it and a long-lasting suprathreshold masking stimulus. Both stimuli were sine-wave gratings of the same vertical orientation and in the peak-subtract phase but differed in spatial frequency by a factor of 3. The temporal masking functions obtained with 2- and 6-cycles/deg maskers of high contrast exhibited transient on- and off-peaks of masking and a sustained effect during the masker exposure. An 18-cycles/deg masker caused sustained masking only. Experiments with maskers of variable spatial frequency and contrast showed that, in the low-spatial-frequency range, the mechanism responsible for the transient effect was more sensitive than that generating the sustained effect, while the sustained effect required less contrast in the high-spatial-frequency range. The results are considered as evidence, in addition to previous findings, for the sustained/transient dichotomy in the temporal domain.