Visual persistence of spatially filtered images

Periodic stimuli such as sine-wave gratings and checkerboard patterns have been used in many studies of visual perception. It is well known that with such stimuli, visual persistence increases as spatial frequency increases and as contrast decreases. It is not clear, however, that similar relationships obtain for aperiodic stimuli such as natural images. Digitized images of objects (a face and a vase) were submitted to two-dimensional Fourier analysis. Four pairs of spatial frequency band-limited images were created for each image. Each pair consisted of a normal (NP) and a scrambled (SP) phase version, with the magnitude spectrum and space-averaged luminance the same within each pair. Filter bandwidths were one octave wide. Threshold persistence was measured for each spatially filtered image. Visual persistence for SP images increased significantly as spatial frequency increased, whereas no significant differences were found for NP images. This suggests that the temporal processing of complex, aperiodic visual images is influenced by the spatial frequency and contrast of local features within the image and cannot be predicted by space-averaged estimates of contrast and spatial frequency.     

A low-cost solid state device for producing delayed auditory feedback

This paper presents a design for construction of a relatively low-cost solid state delayed auditory feedback device. The advantages of this unit are that it is reliable, flexible, easy to operate, and it does not require audio tape.     

Temporal integration of spatially filtered visual images.

Factors which govern the temporal integration of spatial information were examined in a group of five experiments. A series of high-pass and low-pass spatially filtered versions of a visual scene were generated. Observers' ratings of these filtered versions of the scene for perceived image quality indicated that quality was determined both by the bandwidth of spatial information and the presence of high-spatial-frequency edge information. When sequences of three different versions of the scene were presented over an interval of 120 ms the perceived quality of the resulting composite image was determined both from the ratings of the individual components of that sequence and from the order in which these components were presented. When the order of spatial information in a sequence moved from coarse to fine detail the perceived quality of the composite image was significantly better than when the order moved from fine to coarse. This evidence of a coarse-to-fine bias in pattern integration was further investigated with a detection paradigm. The pattern of errors once again indicated that temporal integration of spatial information was superior when a coarse-to-fine mode of information delivery was employed. Taken together the data indicate that the pattern-integration mechanism has an inherent order bias and does not accumulate spatial information so efficiently when the 'natural' coarse-to-fine order is violated.     

A low-cost, MR-compatible olfactometer

We present a design for an olfactometer, suitable for fMRI experiments, that can be constructed at extremely low cost. The olfactometer presents odors directly to the nose via a nasal cannula at unobtrusively low flow velocities, with no large assemblies required on or near the subject’s face. The olfactometer can be controlled manually, or by computer via a serial interface. A validation study verified that the olfactometer reliably presents odors to test subjects. Errors and response latency times decreased with increased flow rate in an orderly manner, as expected.     

A method for producing random visual textures

Textures composed of randomly shaped black and white areas may be produced from high-contrast photographs of a mixture of white and black-dyed rice. Moderate control of black-to-white ratio and many randomizations at a given ratio are possible. This method is cheaper than computer generation and better controlled than the more inexpensive methods.     

The effects of spatial phase on reaction time to spatially filtered images

Summary Many studies of visual perception have used periodic stimuli such as sine-wave gratings and checker-board patterns. It is well known that reaction time (RT) to such stimuli increases with increasing spatial frequency and decreasing contrast. While this is the case with periodic stimuli it is not clear that these relationships obtain for aperiodic stimuli such as natural scenes. A digitized image of an object (a vase) was submitted to two-dimensional Fourier analysis. Four pairs of spatial frequency band-limited images were created for each image. Each pair consisted of a normal-phase (NP) and a scrambled-phase (SP) version, with the magnitude spectrum and space-averaged luminance the same within each pair. Filter band-widths were 1 octave wide. Manual RT was measured for onset and offset of each spatially filtered image. Mean RT for SP images increased significantly with increasing spatial frequency, while no other significant differences were found with the NP images. This suggests that the temporal processing of complex, aperiodic images is influenced by the spatial frequency and contrast of local regions within the image, rather than by the space-averaged contrast of the entire image, and cannot be predicted by global estimates of contrast and spatial frequency.     

A low-cost method for digitizing videotaped continuous movements on the Macintosh

We describe an inexpensive means of digitizing videotaped positions of moving points, such as the positions of the joints of a person who is performing an action. Single-frame video images and a Macintosh computer monitor are optically superimposed, using a half-silvered mirror, and the positions of reference points in the video image are manually clicked in by the operator, so that the screen coordinates of the reference points on each frame can be stored in a text file for later analysis. The digitizing program records comments and identifying information along with the position data.     

A method for producing foveal retinal exposures in an awake,task-oriented,rhesus monkey

A method for producing retinal exposures from a laser source in an awake, task-oriented S is presented. The technique allows for the measurement of rhesus monkey visual acuity immediately following exposures.     

Spatial frequency filtered images reveal differences between masked and unmasked processing of emotional information

High and low spatial frequency information has been shown to contribute differently to the processing of emotional information. In three priming studies using spatial frequency filtered emotional face primes, emotional face targets, and an emotion categorization task, we investigated this issue further. Differences in the pattern of results between short and masked, and short and long unmasked presentation conditions emerged. Given long and unmasked prime presentation, high and low frequency primes triggered emotion-specific priming effects. Given brief and masked prime presentation in Experiment 2, we found a dissociation: High frequency primes caused a valence priming effect, whereas low frequency primes yielded a differentiation between low and high arousing information within the negative domain. Brief and unmasked prime presentation in Experiment 3 revealed that subliminal processing of primes was responsible for the pattern observed in Experiment 2. The implications of these findings for theories of early emotional information processing are discussed.     

A method of producing a three-dimensional cathode ray tube display

A method of producing a true three-dimensional cathode ray tube display has been developed. It has been used to plot three-dimensional vectorcardiograms, bar graphs, and would probably be useful to research in visual perception.     

Configured-groups hypothesis: fast comparison of exact large quantities without counting

Our innate number sense cannot distinguish between two large exact numbers of objects (e.g., 45 dots vs 46). Configured groups (e.g., 10 blocks, 20 frames) are traditionally used in schools to represent large numbers. Previous studies suggest that these external representations make it easier to use symbolic strategies such as counting ten by ten, enabling humans to differentiate exactly two large numbers. The main hypothesis of this work is that configured groups also allow for a differentiation of large exact numbers, even when symbolic strategies become ineffective. In experiment 1, the children from grade 3 were asked to compare two large collections of objects for 5 s. When the objects were organized in configured groups, the success rate was over .90. Without this configured grouping, the children were unable to make a successful comparison. Experiments 2 and 3 controlled for a strategy based on non-numerical parameters (areas delimited by dots or the sum areas of dots, etc.) or use symbolic strategies. These results suggest that configured grouping enables humans to distinguish between two large exact numbers of objects, even when innate number sense and symbolic strategies are ineffective. These results are consistent with what we call “the configured group hypothesis”: configured groups play a fundamental role in the acquisition of exact numerical abilities.     

A low-cost,low-drain signal generator for time-sampling observation

A battery-powered interval timer is described. The low-cost circuit is detailed.     

Geometric specification of dynamics: learning to visually perceive kinetic quantities from static images

In a single experiment, perceivers viewed computer-generated hammer-like objects and estimated a kinetic property. Each hammer comprised a cylinder of some diameter and height, attached to a handle-a second cylinder of fixed diameter and variable length. On 5 blocks of trials, three groups of perceivers reported a property reflecting mass, torque, or moment of inertia. Blocks 2-4 were training blocks on which numerical feedback was given. On blocks 6 and 7, perceivers were asked to report the kinetic properties not reported on blocks 1-5. We were interested in how geometrical object properties affected the perception of kinetic properties, and how that perception changed with experience. To determine how geometrical object properties informed reports of kinetics, a continuous information space of head diameter and height, and handle length was created, and perceivers' loci within that space were determined. Perceivers began at various distances from the optimum for the to-be-reported property and were closer to the optimum after training. On blocks 6 and 7, performance did not reflect transfer from training on another property. The results were interpreted in the context of the theory of direct learning.     

A simple method of producing discrete subcortical lesions using radio-frequency currents

The described procedures represent an evaluation of the use of radio frequency currents in the production of discrete subcortical brain lesions. The methods described and the electrodes used indicated that RF lesion size was closely and linearly related to a simple V dc index and that the resultant lesions were equally distributed around the position of the lesion electrode with extremely smooth and consistent perimeters.     

A method for factoring large numbers of items

The computation of intercorrelation matrices involving large numbers of variables and the subsequent factoring of these matrices present a formidable task. A method for estimating factor loadings without computing the intercorrelation matrix is developed. The estimation procedure is derived from a theoretical model which is shown to be a special case of the multiple-group centroid method of factoring. Empirical checks have indicated that the model, even though it makes some stringent assumptions, can be applied to a variety of variables found in psychological factoring problems. It has been found to be particularly useful in factoring test items.     

Detection of shift in binaural images: A rating method approach

Two practiced listeners were run in a lateralization task in which a rating method was employed. The detection of right and left shifts from the center position was determined. The effect of frequency of the signal was also assessed in the lateralization task. In addition, nine naive listeners were run in a similar situation in order to determine the feasibility of the use of the rating method approach with untrained Ss. First-half, second-half comparisons were determined to check reliability of the technique and also to evaluate the effect of number of trials. The experimental results indicate the procedure is a promising one for the study of directional shifts in binaural stimuli with practiced listeners.