Visual temporal integration and simple reaction time

Intensity-time reciprocity for simple RT to foveal pulses of light was demonstrated up to 11 msec by using two experimental paradigms. The first paradigm was designed to separate two possibly confounded factors displayed by previous studies investigating the effects of increased stimulus duration on RT: (1) an asymptotic RT as a function of the increasing energy of a pulse as its duration is increased, and (2) the breakdown of integration as the pulse duration is increased. The second paradigm was designed to avoid the first factor so as to maximize the possibility of finding partial integration at long durations. In this paradigm, partial integration was demonstrated for additional light input presented as long as 64 msec after stimulus onset. The failure of other studies to demonstrate temporal integration for RT is discussed in terms of these paradigms.     

Binding time: Evidence for integration of temporal stimulus features

Several lines of evidence suggest that during processing of events, the features of these events become connected via episodic bindings. Such bindings have been demonstrated for a large number of visual and auditory stimulus features, like color and orientation, or pitch and loudness. Importantly, most visual and auditory events typically also involve temporal features, like onset time or duration. So far, however, whether temporal stimulus features are also bound into event representations has never been tested directly. The aim of the present study was to investigate possible binding between stimulus duration and other features of auditory events. In Experiment 1, participants had to respond with two keys to a low or high pitch sinus tone. Critically, the tones were presented with two different presentation durations. Sequential analysis of RT data indicated binding of stimulus duration into the event representation: at pitch repetitions, performance was better when both pitch and duration repeated, relative to when only pitch repeated and duration switched. This finding was replicated with loudness as relevant stimulus feature in Experiment 2. In sum, the results demonstrate that temporal features are bound into auditory event representations. This finding is an important advancement for binding theory in general, and raises several new questions for future research.     

Set and temporal integration

An experiment was conducted to explore the temporal structure of set formation in a complex reaction time (RT) task. On each trial an instruction [I-event] was given telling Ss whether identity of color or form on a separately presented alternative display (A-event) was the dimension relevant on that trial. The A-event consisted of a pattern of four colored forms. The two forms on one side were matched for color and on the other side for form. S’s task was to depress one of two keys. The correct key was homolateral to the matched relevant dimension. The basic independent variable was the time interval separating the I- and A-events (ISI). At short ISIs, RT wasa linear function oflSI with slope equal to -0.5. RT was independent of the order in which the events occurred at short ISIs, although at longer ISIs (3 sec) RT was longer when the A-event followed the I-event. Also, RT was shorter at short ISIs when color was the relevant dimension rather than form. although this difference disappearedat longer ISIs. The results were discussed in relation to information processing models and previous research dealing with partialadvance information.     

Visual temporal integration for threshold,signal detectability,and reaction time measures

A comparison was made of temporal integration for three different response measures in a visual detection task: (1) response frequency, (2) signal detectability as measured for rating ROC curves. (3) simple reaction times (RTs). These measures were obtained on the same trials, to the same stimuli-orange (581 rim) light pulses of 50 min of visual angle fixated foveally and presented to dark-adapted Os in a monocular Maxwellian view. All three response measures showed a period of luminance-duration reciprocity (Bloch’s law), followed by a period of partial integration. The end points of luminance-duration reciprocity (critical duration) and partial integration (utilization time) were shorter for RTs than for the response frequency and signal detectability measures. Neurophysiological.implications of differences in time constants of integration for RT and psychophysical measures are discussed.     

Reaction time measurement errors resulting from the use of CRT displays

Three sources of potential error in reaction time measurement may occur when raster scan CRT displays are used to present stimuli: phosphor persistence, sweep delay, or transmission delay. For most applications, only the third source of error is likely to be significant.     

Visual form integration and discontinuity detection

Two experiments were conducted to determine if discontinuity detection limits the visual integration of two stimuli presented successively. If this is the case, then presenting two dim stimuli should permit better integration than presenting two bright stimuli. In Experiment 1, five observers named the position of the missing dot in a 5 x 5 dot matrix. Twelve randomly selected dots were presented in each of two stimulus presentations. The stimuli varied in intensity in a ratio of 15:1 and stimulus onset asynchrony (SOA) varied between 50 msec and 80 msec. At the longer SOAs, presenting two bright stimuli led to a higher percentage of correct responses than presenting two dim stimuli. There was no difference between those conditions at the shorter SOAs. In Experiment 2, 12 naive observers rated the amount of integration of the same stimuli on a 7-point scale, under the same presentation conditions. Rated integration was higher with two dim stimuli than with two bright stimuli. These apparently contradictory results are explained in terms of Hawkins and Shulman's distinction between two kinds of visual persistence. It is concluded that subjects can respond to integration and discontinuity detection separately. No evidence was found that discontinuity detection limits the integration.     

Spatial and temporal frequency in figure-ground organization

Figure-ground organization of an ambiguous pattern can be manipulated by the spatial and temporal frequency content of the two regions of the pattern. Controlling for space-averaged luminance and perceived contrast, we tested patterns in which the two regions of the ambiguous pattern contained sine-wave gratings of 8, 4, 1, or 0.5 cycles per degree (cpd) undergoing on:off flicker at the rates of 0, 3.75, 7.5, or 15 Hz. For a full set of combinations of temporal frequency differences, with each spatial frequency the higher temporal frequency was seen as background for more of the viewing time. For two spatial frequency combinations, 1 and 4 cpd, and 1 and 8 cpd, tested under each of the four temporal frequencies, the lower spatial frequency region was seen as the background for more of the viewing time. When the effects of spatial and temporal frequency were set in opposition, neither was predominant in determining perceptual organization. It is suggested that figure-ground organization may parallel the sustained-transient response characteristics of the visual system.     

Electrocutaneous psychophysical input-output functions and temporal integration

Electrocutaneous magnitude estimation functions were generated by stimuli ranging from 1.0 to 5.0 mA and from 100 to 6,400 msec in duration. The results indicate that when these functions are fitted by a two-parameter power function (ME = aI^b), the values of the constant, a, and the exponent, b, are altered by increases in stimulus duration, with a increasing and b decreasing. The exponent decreases from around 1.4 to 0.93 as duration increases from 100 to 6,400 sec. Equal magnitude estimation contours drawn for estimates ranging from “2“ to “50“ can be fitted by an equation representing partial integration, I × t^a = K. The exponent a decreases as a function of the level of the magnitude estimation, indicating less partial integration at higher than at lower levels of estimated magnitude. The electrocutaneous data are compared to data in other sensory modalities.     

Five-month-old infant recall and utilization of temporal organization

The ability of 5-month-old infants to recall temporal information and utilize temporal organization was investigated in two experiments. Infants were trained to fixate a hierarchically structured or an unstructured sequence of stimuli which appeared in four spatial positions. In the first study, the number of infants who demonstrated correct recall through the third serial position of a sequence was significantly better then would occur by chance. In the second study, infants given structured sequences showed a significant increase in the number of correct fixations across trials, and they recalled across serial positions better in structured sequences. Also, accuracy of recall in both studies for the middle serial positions was related to hierarchical organization following 8-unit structured sequence training but was at chance level following unstructured sequence training. Results of both studies were interpreted within a temporal organizational framework: Infants appear to utilize organization within sequences of information.     

Cortical dynamics of visual persistence and temporal integration

In a temporal integration experiment, subjects must integrate two visual stimuli, presented at separate times, to perform an identification task. Many researchers have assumed that the persistence of the leading stimulus determines the ability to integrate the leading and trailing stimuli. However, recent studies of temporal integration have challenged that hypothesis by demonstrating that several theories of persistence are incompatible with data on temporal integration. This paper shows that an account of visual persistence given by a neural network model of preattentive vision, called the boundary contour system, explains data on temporal integration. Computer simulations of the model explain why temporal integration becomes more difficult when the display elements are separated by longer interstimulus intervals or are of longer duration or of higher luminance, or are spatially closer together. The model suggests that different mechanisms underlie the inverse duration effects for leading and for trailing elements. The model further predicts interactions of spatial separation, duration, and luminance of the trailing display.     

Monaural and binaural temporal integration of noise bursts

Summary A comparison was made between monaural and binaural temporal integration of noise bursts at threshold. The data indicate partial integration, with approximately a 6 dB decrease in threshold per decade increase in noise burst duration for both conditions of stimulation (i.e., parallel functions) for durations ranging from 4 to 256 msec. When thresholds in dB are plotted as a function of log duration, the linear component accounts for 99% of the data indicating no essential change in the partial integration functions up to at least 256 msec. The intercept difference between the monaural and binaural integration functions is 2.5 dB.     

Fast temporal dynamics of visual cue integration

The integration of information from different sensors, cues, or modalities lies at the very heart of perception. We are studying adaptive phenomena in visual cue integration. To this end, we have designed a visual tracking task, where subjects track a target object among distractors and try to identify the target after an occlusion. Objects are defined by three different attributes (color, shape, size) which change randomly within a single trial. When the attributes differ in their reliability (two change frequently, one is stable), our results show that subjects dynamically adapt their processing. The results are consistent with the hypothesis that subjects rapidly re-weight the information provided by the different cues by emphasizing the information from the stable cue. This effect seems to be automatic, ie not requiring subjects' awareness of the differential reliabilities of the cues. The hypothesized re-weighting seems to take place in about 1 s. Our results suggest that cue integration can exhibit adaptive phenomena on a very fast time scale. We propose a probabilistic model with temporal dynamics that accounts for the observed effect.     

The role of attention in temporal integration

When two visual patterns are presented in rapid succession, their contours may be combined into a single unified percept. This temporal integration is known to be influenced by such low-level visual factors as stimulus intensity, contour proximity, and stimulus duration. In this study we asked whether temporal integration is modulated by an attentional-blink procedure. The results from a localisation task in experiment 1 and a detection task in experiment 2 pointed to two separate effects. First, greater attentional availability increased the accuracy of spatial localisation. Second, it increased the duration over which successive stimuli could be integrated. These results imply that theories of visible persistence and visual masking must account for attentional influences in addition to lower-level effects. They also have practical implications for use of the temporal-integration task in the assessment of group and individual differences.     

Role of spatial and temporal coincidence in depth organization

The linking of spatial information is essential for coherent space perception. A study is reported of the contribution of temporal and spatial alignment for the linkage of spatial elements in terms of depth perception. Stereo half-images were generated on the left and right halves of a large-screen video monitor and viewed through a mirror stereoscope. The half-images portrayed a black vertically oriented bar with two brackets immediately flanking this bar and placed in crossed or uncrossed disparity relative to the bar. A pair of thin white 'bridging lines' could appear on the black bar, always at zero disparity. Brackets and bridging lines could be flickered either in phase or out of phase. Observers judged whether the brackets appeared in front of or behind the black bar, with disparity varied. Compared to conditions when the bridging lines were absent, depth judgments were markedly biased toward "in front" when bridging lines and brackets flashed in temporal phase; this bias was much reduced when the bridging lines and brackets flashed out of phase. This biasing effect also depended on spatial offset of lines and brackets. However, perception was uninfluenced by the lateral separation between object and brackets.     

Electrocutaneous stimulation: Psychometric functions and temporal integration

Psychometric functions and psychophysical strength-duration curves were obtained with rectangular electro-cutaneous pulses. The slopes of the psychometric functions were much steeper than corresponding functions in other modalities, with the standard deviation of the distribution only about 0.08 times the threshold. Precise monitoring of stimulus current showed that physiological rather than physical variability was involved. Psychophysical strength-duration curves support the contention that large A-fibers are directly stimulated. Data from this study. as well as from comparable I × t experiments in other senses, are well-fit throughout the range of durations by rectangular hyperbolas. The period over which complete temporal summation occurs is only about 0.5 msec.