Apparent haptic movement

When Os were presented with ISO-Hz vibrotactile bursts at two loci on the skin of the thigh and permitted to adjust the time between burst onsets, they reported good apparent movement between the loci. The time between stimulus onsets for optimal movement was found to vary directly with the duration of the stimulus. Replication of the experiment with electrocutaneous stimuli at 1 KHz yielded similar results. Comparison of the data with results from a study of visual apparent movement revealed no difference between the two modalities for the relationship between stimulus onset intervals and stimulus duration. The significance of the results for hypotheses about the processes underlying perception of apparent movement is discussed.     

Apparent haptic movement

When as were presented with 150-Hz vibrotactile bursts at two loci on the skin of the thigh and permitted to adjust the time between burst onsets, they reported good apparent movement between the loci. The time between stimulus onsets for optimal movement was found to vary directly with the duration of the stimulus. Replication of the experiment with electrocutaneous stimuli at 1 KHz yielded similar results. Comparison of the data with results from a study of visual apparent movement revealed no difference between the two modalities for the relationship between stimulus onset intervals and stimulus duration. The significance of the results for hypotheses about the processes underlying perception of apparent movement is discussed.     

On the relation between metacontrast masking and suppression of visible persistence

Does the introduction of additional contours in a display sequence (an operation known to reduce the strength of suppression in metacontrast) also reduce suppression of visible persistence? In three experiments, duration of visible persistence was estimated by a method in which successful performance depends on the temporal integration of a pattern whose elements are displayed in two successive frames. In this procedure, the arrival of the trailing frame is known to exert a suppressive influence on the visible persistence of the leading frame. Embedding the elements of the leading frame within additional contours (a line grid) reduced the degree of suppression exerted by the trailing frame. This did not occur when the grid was part of the trailing display. We conclude that suppression of visible persistence and metacontrast masking belong to the same class of events.     

An analysis of U-shaped metacontrast

Using a brightness-discrimination task similar to that employed by Bernstein, Proctor, Proctor, and Schurman (1973), masking functions were obtained in two experiments. In Experiment I, test stimulus (TS) and mask stimulus (MS) energies were held constant but luminance and duration were varied reciprocally. The obtained masking functions, plotted as a function of stimulus onset asynchrony (SOA), were of an essentially identical U shape. This suggests that (a) SOA is a more suitable measure of delay than interstimulus interval, and (b) Bloch’s law holds for the requisite discrimination. In Experiment II, TS luminance and MS luminance were varied independently. This was to see whether the MS served as a frame of reference at short SOA, as suggested previously (Bernstein et al, 1973). The results were that this was, in fact, the case and that the transition from comparative to absolute judgment strategies as SOA increases is a major contributor to U-shaped masking functions.     

Apparent movement and the Brown-Voth experiment

An experiment on apparent movement reported by Brown and Voth and referred to by Osgood and Bartley was repeated. The results obtained differed from those reported by Brown and Voth, but exhibited phenomena not described by them. Further experiments derived from their theories were also carried out, the results failing to support Korte's laws and raising some new points.     

Effects of absolute mask energy and mask energy range on metacontrast suppression

In an experiment similar to one by Bernstein, Fisicaro, and Fox (1976), subjects were asked to judge the brightness of test stimuli in a metacontrast display. The energies of the test and of the mask varied orthogonally. Various experimental conditions differed with respect to the range of mask energies. Individually, the mask energies were generally weaker than the test energies. The results replicated the main findings of Bernstein et al. (1976) in that judgments of the test were negatively correlated with mask energy at short stimulus onset asynchrony (SOA) but positively correlated at long SOA. These effects were more pronounced when the masks were similar in energy range and level to the tests than when they were wider in energy range and weaker. In general, there was no evidence for the effects of trial-to-trial variation described by Hake, Faust, McIntyre, and Murray     

Apparent movement induced by afterimages

A small light source viewed in the dark through an afterimage produced by an electronic flash may appear to move along short random paths. Experiment 1 shows that this is not an instance of the autokinetic phenomenon, and experiment 2 shows that it is not related to the 'fluttering hearts' phenomenon. On the basis of experiments 1 and 3 it is concluded that small-scale ocular drifts, microsaccades, and possibly tremors cause the whole afterimage to move. The afterimage serves as a frame of reference and induces movement of the light source.     

Apparent movement in tridimensional space

The space-time relationships satisfying Korte’s third law of apparent movement were studied in three experiments. The results generally confirm and extend Corbin’s conclusion that apparent movement is not a projection-level phenomenon, but one involving spatial constancy, i.e., some representation of tridimensional space. Between situations in which the stimuli were retinally matched, the time interval necessary, for apparent movement varied w~th their phenomenal separation, whether the latter was determined by the distance of stimuli from the O, deviation of sttmuli from the frontal plane, or illusory slant of the stimulus plane produced by a perspective gradient.     

Apparent movement in phenomenal space

The spatial and temporal variables in Korte’s third law of apparent movement were studied in pictorial arrays in which size constancy could be expected to prevail. The thresholds for apparent movement were determined under conditions in which two squares appeared on a plane either with or without perspective information for depth. The results suggest that apparent movement varies with the perceived depth separation only if the size of the stimulus pair is congruent with contextual depth representations. The obtained psychophysical function relating thresholds for third-dimensional movement to pictorial depth scale supports the view that apparent movement preserves gradient-of-texture information.     

A tactile metacontrast effect

Vibrotactile patterns, generated on the 6×24 array of the Optacon, were presented to subjects’ left index fingertips. The subjects identified these patterns in the absence of any masking stimuli and in the presence of spatially adjacent masking stimuli. The amount of interference in recognizing the patterns was measured as a function of the interval between target and masker onsets. Masking functions similar to those reported in visual metacontrast studies were found; that is, more masking occurred when masker onset followed target onset by 25 to 50 msec than when onsets were simultaneous. Subjects showed more metacontrast when masker energy was reduced, a finding paralleled in the visual literature. The relevance of some models of visual metacontrast to the tactile findings is discussed.     

Apparent movement detection in the pigeon

Pigeons were trained to discriminate between the presence and absence of apparent movement in visual displays. Generalization gradients obtained on the dimension of speed indicated a broad range of movement detection. Extremely accurate discrimination performance on displays varying in direction of movement suggested formation of a "movement concept".     

Apparent size and duration of a movement after-effect

Four experiments were performed to study the relationship between Emmert's law and the duration of the movement after-effect (MAE). The duration of the MAE increased with increased distance of the test field; this result was shown to be produced by the correlative change in apparent size of the after image. The effect did not occur when cues for distance judgments were reduced. Reducing the duration of the MAE suppressed the variation in its duration at varying distances of the test field. Some implications for the mechanism of the MAE are discussed.     

Tactile suppression in goal-directed movement

Sharing numerous characteristics with suppression in the other senses, tactile suppression is a reliable phenomenon that accompanies movement. By investigating the simplest of movements (e.g., finger flexions), early research tried to explain the origins of the phenomenon in terms of motor command generation together with sensory reafference. Here, we review recent research that has delved into (naturalistic) goal-directed movements. In connection with goal-directed movement, tactile suppression is evident as a decrease in behavioural performance measured shortly prior to, and during, movement execution. It is also reflected in a consistent response bias highlighting the (perceptual) uncertainty of the movement. Goal-directed movement supports the forward model and establishes contextual influences as the defining influences on tactile suppression. Depending on the task at hand, people prioritize a certain percept during movement. Future research, we argue, should focus on studying naturalistic movements, or sequences of movements, that share a common meaning or goal.     

Metacontrast suppression and criterion content: A discriminant function analysis

Three test and three mask energies of a metacontrast display were varied orthogonally and randomly over trials. The stimulus onset asynchrony (SOA) separating them was varied over blocks of trials from 0 to 180 msec in 30-msec steps. Both the accuracy in judging the test and the coherence (consistency) of the judgments were U-shaped functions of SOA. Thus, metacontrast suppression is in part due to inadequate information. In addition, mask energy was found to correlate negatively with judgments of the test at short SO As but positively at longer SOAs. This indicates that part of the masking effect is due to inappropriate use of information. Certain similarities were noted between these findings and those obtained with judgments of frequency in the auditory-recognition masking paradigm. In general, the results indicate that subjects respond to different features of the stimulus situation as SOA varies.     

A decisional component of holistic encoding

It has been proposed (see, specifically, M. J. Farah, K. D. Wilson, M. Drain, & J. N. Tanaka, 1998) that human faces are used in cognition as undifferentiated wholes. General recognition theory (GRT; F. G. Ashby & J. T. Townsend, 1986) is used to represent hypotheses regarding the possible sources for the behavioral evidence supporting holistic representation. Specifically, it is suggested that holism can be understood in terms of violations of informational independence, informational separability, or decisional separability, as these constructs are defined in GRT. Stimuli were presented upright, inverted, and in an encoding task that emphasized the meaningful nature of the stimuli. Patterns of performance (recognition hit rates) were consistent with prior studies. However, there were only a handful of violations of informational separability. Instead, consistent violations of decisional separability suggested a decisional basis for holistic effects.     

A signal-detection approach to subception: Concomitant verbal and finger-latency responses in metacontrast

Metacontrast conditions were created by the onset of flanking lights designed to mask the prior blink of an otherwise steady center light. For pseudometacontrast trials, the center light did not blink in advance of the flanking lights. Responses were an immediate finger-key release to the first detectable change in the visual display followed by a statement of whether the center light had been doused. A signal-detection analysis was used to avoid both threshold and response-criterion problems. Verbal report was, on the average, more sensitive than finger latency in detecting the masked blinks. However, there were large and consistent individual differences; reaction time was the more sensitive for a few subjects. Data analysis revealed that each response system showed detection with the other system “partialed out.” A model was offered in which verbal- and finger-response systems act in parallel, with uncorrelated variability between systems accounting for the subception effect.