Immediate and delayed recognition of sequentially presented random shapes.

Two experiments tested whether short-term memory accounts for the recency effect observed with rapid sequential presentation of nonverbal stimuli. Four random shapes were presented sequentially (with no interstimulus interval) on each trial at rates of 150 msec, 250 msec, 500 msec, and 1,000 msec per stimulus. Subsequent recognition varied positively with exposure duration, ranging from 57% at 150 msec to 77% at 1,000 msec. Two serial position effects were observed: a slight decrease in recognition accuracy for the first stimulus in each sequence and a large increase in recognition for the last stimulus in each sequence. The recency effect was not altered by an intervening 30-sec delay, an intervening 30-sec copying task, or an intervening 30-sec copying and counting task. Since neither visual nor verbal distractors altered recognition accuracy, it was suggested that all shapes were processed directly into long-term memory storage. It also was hypothesized that long-term storage of a nonverbal stimulus requires identification of a distinctive feature of the stimulus and that this process may continue for a brief period after actual stimulus offset.     

Visual form recognition threshold and the psychological refractory period

Two experiments studied the effect of a reaction time response (RT) on visual form recognition threshold when the temporal interval separating the RT stimulus and the recognition stimulus was short. In Experiment 1 an initial RT response to an auditory signal did not impair the subsequent forced-choice visual form recognition threshold. Interstimulus intervals (ISI) of 0, 50, 100, 150, and 200 msec were used; S was always aware of the ISI under test. In Experiment 2 a visual stimulus was used to elicit the R T response; this shift to an intramodal stimulus did not alter the recognition threshold. These data were interpreted as supporting the hypothesis that two stimulus events can be processed simultaneously even when the temporal interval between them is short.     

The effect of somaesthetic and acoustic stimuli on the threshold of fusion of paired light flashes in human subjects

The threshold of fusion of paired flashes of light was measured by determining the largest interval between two flashes of light at which they were reported as one and not as two flashes. When a weak electric shock to the skin was presented at the same time as the first flash, the threshold was increased compared to the threshold measured when the flashes were unaccompanied by a shock. As the interval between shock and first flash was increased up to 600 millisec, the effect diminished. A similar pattern of results was obtained using a click, instead of a shock as the additional stimulus. The effect on the two-flash threshold of varying click intensity was also studied. No retroactive effects of the shock on the two-flash threshold were observed.     

Differential backward masking of words and letters by masks of varying orthographic structure

The effects of structural relationships between targets and masks were investigated using a backward-masking paradigm. Specifically, the masking of single letters, common fiveletter words, and five-letter pseudowords masked by a blank flash, strings of overlapped letters, pseudowords, and words was investigated. Target duration was varied from 2 to 32 msec, with mask duration held constant at 25 msec. The dependent measure was the critical interstimulus interval for correct target identification. Letters were more effectively masked than words and pseudowords. A blank mask caused the least amount of masking, followed by the overlapped letter strings, and then the word and pseudoword masks. In addition to the overall greater masking effectiveness for the three patterned masks, overlapped letter strings masked letters more effectively than they did words. The implications of current theories of masking for these results and the implications of these results for theories of word recognition were discussed.     

The discrimination of differences in duration of a thermal reinforcement

The sides of a contour square appear successively when context lines are presented one before and one after the square. As the interstimulus interval (ISI) between lines and square is increased to 140 msec, reports of succession increase. If the sides of the square are presented successively and interpart interval (IPI) varied by a single staircase method in order to determine a succession threshold, the average magnitude of this threshold varies as a function of ISI, decreasing up to 140 msec lSI. Each S, however, shows a maximum decrease in threshold between 80 and 120 msec. Reports of this illusion are not dependent on beta movement of either context lines or square.     

The intervals at which homogeneous flashes recover masked targets

The recovery effect may be induced by the introduction of a homogeneous blank flash after a patterned mask. It is not clear which parameters optimize the effect. In this study, the effect of systematical variation of the different interstimulus intervals on performance was investigated. Conditions in which the blank flash preceded the patterned mask were included. The important parameter is shown to be the interval between Mask 1 and Mask 2. For optimal recovery, this value has to be 0–20 msec. It is argued that these results, as well as a number of other recovery findings, can be explained by the suppressing influence of homogeneous flashes on contour processing channels in the visual system.     

Reversing the picture superiority effect: A speed—accuracy trade-off study of recognition memory

Speed-accuracy trade-off methods have been used to contrast single- and dual-process accounts of recognition memory. With these procedures, subjects are presented with individual test items and required to make recognition decisions under various time constraints. In three experiments, we presented words and pictures to be intentionally learned; test stimuli were always visually presented words. At test, we manipulated the interval between the presentation of each test stimulus and that of a response signal, thus controlling the amount of time available to retrieve target information. The standard picture superiority effect was significant in long response deadline conditions (i.e., > or = 2,000 msec). Conversely, a significant reverse picture superiority effect emerged at short response-signal deadlines (< 200 msec). The results are congruent with views suggesting that both fast familiarity and slower recollection processes contribute to recognition memory. Alternative accounts are also discussed.     

Retroactive contour enhancement: A new visual storage effect

A test stimulus (a visual form) which is below recognition threshold when flashed briefly against a steady background field can be raised to complete discriminability if the background field is terminated and replaced by darkness within about 100 msec of the test flash. There must therefore be an efficient storage process for the apparently “invisible” form. The phenomenon is shown to occur under a variety of conditions. It appears not to be a simple visual masking phenomenon. The tasks used are forced-choice, and the phenomenon provides a new demonstration of visual storage effects which previously have generally been reported only for supraliminal visual test stimuli.     

Duration estimates of two information processing components

Adult humans attempted to make quick responses to the first of two sequentially presented visual stimuli. At short interstimulus intervals (less than about 100 msec) accuracy was impaired by a different second stimulus and this was hypothesized to reflect the activity of an information processing component concerned with stimulus registration. At longer interstimulus intervals (up to approximately 350 msec) reaction time was inhibited by a different second stimulus and this was assumed to reflect the activity of a second component concerned with decision. The stimulus registration component was insensitive to variations in the complexity of the task, while the decision component was found to be greater for a task requiring recognition (is the current stimulus the same as an earlier one?) than for one merely requiring choice (what is the current stimulus?). This functional independence and the sizeable difference in the temporal range of susceptibility led to the conclusion that two distinct information processing components were involved.     

Auditory backward recognition masking: effect of interaural phase on masker efficacy

The effect of interaural phase on pitch and lateralization recognition was examined. Tonal signals were followed by a variable interstimulus interval and an interference tone. Stimuli were presented in a binaural masking-level difference paradigm as a means of manipulating the perceptual location of the signal within the head. In separate tasks, subjects were required to recognize the pitch or location of the signal. The pitch-recognition task resulted in the expected increase in performance as the interstimulus interval increased. There was no effect of interaural phase on pitch-recognition performance. There was no significant effect of interstimulus interval on performance in location recognition. Subjects were proficient at recognizing location of the signal regardless of the interstimulus interval. The data suggest that a strict single-channel interpretation of the preperceptual storage model of backward auditory recognition is inadequate.     

Event-related potentials, semantic processes, and expectancy factors in word recognition

Electrophysiological activity was recorded at 16 scalp locations during a word recognition task in order to investigate the effect of expectancy factors on ERPs. In each of 160 trials two stimuli (S1 and S2) were presented with a stimulus onset asynchrony (SOA) of 1500 msec. There were four experimental conditions. In the word-antonym (W-A) and the word-nonantonym (W-NA) conditions, both S1 and S2 were words. The subjects' task was to think of the antonym to S1 and respond as fast as possible after the presentation of S2 by pressing a "YES" button if S2 was an antonym to S1 (in the W-A trials), or a "NO" button if S2 was not an antonym to S1 (in the W-NA trials). In the nonword-word (NW-W) and nonword-nonword (NW-NW) conditions S1 was a nonword, while S2 was either a word (in NW-W trials) or a nonword (in NW-NW trials). If S1 was not a word, the subjects were instructed to wait for S2, and respond as fast as possible by pressing the "YES" button if it was a word an the "NO" button if it was not a word. EEG was sampled during a time epoch that started 100 msec before the onset of S1 and continued for another 2560 msec. The ERPs were analyzed separately for each experimental condition and for time epochs related to S1, to S2, and to the SOA. Expected antonyms were recognized significantly faster than any other words or nonwords. The RTs to words in the W-NA and NW-W condition, and to nonwords in the NW-NW condition did not differ significantly from each other. The ERP difference between the four conditions following S2 was interpreted in terms of a negative-going potential which appeared prior to the P300, during a time period which started 200 msec and ended 550 msec from stimulus onset. The negativity related to nonwords was significantly larger than the negativity related to words. The negativity related to the expected antonym was almost nonexistent. It is speculated that this negativity has the same origin as N400, and that it might be related to the process of lexical access.     

Some temporal factors in the successive comparison of auditory amplitudes.

Under certain conditions the discrimination of successively presented auditory amplitudes appears to be primarily a function of the time intervals between stimulus onsets rather than of either the duration of the stimulus or the silent interval between the tones (interstimulus interval). The results of this study are interpreted in terms of a model containing an acquisition process which continues for a set interval (about 600 msec) subsequent to the onset of the stimulus, even if stimulus offset occurs prior to this time. The onset of another stimulus during this period terminates acquisition. The model also includes a memory process which does not start until acquisition is complete.     

Two-flash thresholds as a function of flash luminance and area

Two-flash thresholds were obtained from three dark-adapted Ss by means of a two-interval, temporal forced-choice technique involving foveally fixated circular targets varying in luminance and area. The Ss were instructed to report the temporal position of the longer of two pairs of I-msec flashes. a comparison pair with an interflash interval of 1 msec, and a test pair with a varying interflasn interval. The Ss were informed about the accuracy of their responses after each response. For all three Ss the results replicated a previous finding that two-flash thresholds are a negatively accelerated function of flash luminance. but the function was shown to be dependent on area. a greater threshold change occurring at smaller areas. Two-flash thresholds were also found to be a decreasing function of stimulus area. with the greatest threshold change occurring at low luminances.     

The role of lateral masking and orthographic structure in letter and word recognition.

The present experiments evaluated the contribution of orthographic structure and lateral masking in the perception of letter, word, and nonword test displays. Performance was tested in a backward recognition masking experiment in which a masking stimulus followed the test display after a variable blank interstimulus interval. In agreement with previous findings across different experiments, words were recognized better than single letterd at short interstimulus intervals, but the opposite was the case at long intervals. Performance on the nonwords resembled performance on letters at short masking intervals and performance on words at long masking intervals. The quantitative results were described by a processing model that incorporates the effects of lateral masking and orthographic structure in the dynamic processing of letter strings. Lateral masking tends to lower the potential perceptibility of letters whereas orthographic structure can reduce the uncertainty of the candidate letters in the letter sequence. The present model predicts that the quantitative contribution of each of these processes to performance is critically dependent upon the processing time available before the onset of the masking stimulus.     

Enhancement and summation in the perception of two successive vibrotactile stimuli

Enhancement and summation were found to be fundamentally different perceptual processes affecting the sensation magnitude of two successive vibrotactile stimuli. Enhancement, defined operationally as an increment in the subjective magnitude of one stimulus due to the presentation of a prior stimulus, and summation, defined as an increment in overall subjective magnitude of the two stimuli, were measured for sinusoidal vibration of the thenar eminence of the hand. The effect of summation was maximum when the two stimuli greatly differed in frequency, whereas maximum enhancement effects were found when both stimuli were close in frequency. The summation effect showed little decay as the interstimulus interval was increased to as much as 500 msec, whereas enhancement effects decayed to zero at approximately 500 msec. Results were similar to those obtained in comparable studies of audition and support the hypothesis that there are at least two distinct information-processing channels for the perception of cutaneous vibration.     

Direct measures of short-term visual storage

Two experiments, involving seven conditions, explored the use of direct measures of visual persistence. In each, the subject was asked to judge if an intermittent stimulus appeared perceptually continuous, or whether it completely faded before the next presentation occurred. The first experiment showed that visual persistence was set at approximately 250 msec. for a recycling presentation of a circle in a tachistoscope; in another task employing a moving opaque slit passing back and forth over a circle, persistence times averaged 50 msec. longer. Reducing luminance by 2 log units increased persistence only slightly, though removing the adapting field increased it by over 100 msec. The second experiment, using the repeating circle, varied the duration of the stimulus, and compared monoptic with dichoptic presentations. Visual persistence was found to be independent of stimulus duration over a range of 4 to 200 msec., where all durations were above recognition threshold for the stimulus. Persistence was unaffected whether the stimulus was repeatedly presented in the same eye or alternated between eyes, strongly suggesting that the storage is central. Finally, a re-analysis of Dodwell and Engel's paper on stereopsis suggests that their effects can be adequately explained by visual persistence of the asynchronous stereo pairs, rather than a more complex fusion model. All of these results strongly support the use of visual persistence as a direct measure of short-term visual storage.     

Evidence for visual persistence during saccadic eye movements

Summary 1. The persistence of visual perception was investigated under conditions of visual fixation as well as eye movement. The Ss' task was to discriminate brief double light impulses; their responses were recorded as a function of the duration of the interstimulus interval. Based on these data the critical interstimulus interval was calculated, which yielded equal response frequencies for the perception of one or two stimuli upon presentation of double light pulses.2. In the condition of visual fixation the two stimuli could not be discriminated until the mean value of interstimulus interval exceeded 73 msec. In the condition with eye movements, when the first stimulus was presented in the parafoveal region of the retina before the beginning of the saccade and the second stimulus in the foveal region just after termination of the eye movement, this duration was shown to be statistically of the same magnitude (76 msec).3. Possible alternative interpretations of this latter result, e.g., that it could be explained in terms of masking or saccadic suppression rather than visual persistence was discussed; it was attempted to invalidate such explanations by means of three control experiments.4. The main result, the persistence of visual perception during voluntary eye movements, was discussed in relation to the problem of spatial and temporal stability of visual perception.I thank Prof. Dr. H.W. Wendt for support in correcting the English translation.     

Strategic influence on the time course of predictive inferences in reading

In the present study, we investigated how reading strategies affect the time course of online predictive inferences. Participants read sentences under instructions either to anticipate the outcomes of described events or to understand the sentences. These were followed by a target word to be named, with stimulus onset asynchronies (SOAs) of 500 or 1,000 msec (50- or 550-msec interstimulus interval, respectively). Sentences either were predictive of events or were lexically matched control sentences. There was facilitation in naming latencies for predictable target words in the strategic-anticipation condition at both SOAs, but not in the read-to-understand condition, with a significant improvement in the former condition in comparison with the latter. This suggests that predictive inferences, which are typically considered to be resource demanding, can be speeded up by specific goals in reading. Moreover, this can occur at no cost to comprehension of explicit information, as was revealed by a comprehension test.     

Simultaneous visual events show a long-range spatial interaction

A stimulus consisting of two brief flashes separated by a short interval appears to flicker, whereas a single brief flash does not. Performance on a task requiring discrimination of double and single stimuli is adversely affected by simultaneous presentation of a second, similar stimulus at a relatively remote position in the visual field. Most errors occur when target and mask follow different time courses, one double and the other single. The results of four experiments studying this interaction are reported. An effect on performance is observed under binocular, monocular, and dichoptic viewing conditions. Performance is affected up to target to mask distances of at least 20 deg of arc. Performance increases as target-to-mask onset asynchrony is increased, reaching asymptote at asynchronies of between 100 and 150 msec. The precise shape of the stimuli does not appear to be important in determining the size of the effect or whether or not an effect occurs. An analogy between this effect and apparent movement is suggested.     

The interaction of word frequency and stimulus quality in the lexical decision task: Now you see it, now you don't

Two experiments are reported that examined the joint effects of word frequency and stimulus quality in the context of a lexical decision task. In the first experiment the interval between response to a stimulus and onset of the next stimulus was 0.8 sec, and the effect of the two factors was additive. In the second this interval was 3.3 sec, and the effect of reducing stimulus quality was greater for infrequent words than for frequent words. This is similar to the result of Norris (1984). The inability of current models of word recognition to explain this finding is discussed.