Visual vs. verbal stimulus set in a letter-classification task

In three experiments, subjects classified briefly presented letters as belonging to either the first or the second half of the alphabet. Prior to each target letter, the subjects were given either a verbally named letter (verbal set), a letter presented visually for 3 sec (visual set), or no prior alternative (control). The target was equally likely to be the same as the prior alternative (same trials) or from the opposite half of the alphabet (different trials). Classification accuracy was always greater for visual set than for the control condition. Verbal-set accuracy was no better than control accuracy when the verbal alternative immediately preceded the target but was equal to visual-set accuracy when the alternative preceded the target by 3 sec. In both set conditions, subjects tended to choose the same half of the alphabet as the prior alternative. It was concluded that type and timing of prior alternatives are important variables in accounting for enhanced classification accuracy.     

Fast visual generation: its nature and chronometrics.

The fast-generation model for the matching of mixed-case letter pairs (e.g., Aa, Ab) states that one or both members of a pair activate visual representations in memory of the opposite case, supporting "same" or "different" responses through crossmatching to representations of the pair members themselves. Here the reaction time and error results of three experiments using simultaneous matches support a specific variant of the model in which generation proceeds from the uppercase letter. Furthermore, a manipulation of stimulus onset asynchrony in a fourth experiment using near-simultaneous matches indicates that fast generation produces a visual representation that occurs within 67 msec of initiation and that decays within 200 msec. A fifth experiment contrasts simultaneous and successive matches and in the case of successive matches finds evidence in support of a regeneration process acting after an initial decay. Models of mixed-case matching that are based on the phonetic representation of letter names, or on abstract-letter identities, completely fail to account for the results. Fast generation is distinguishable from slow generation in that it shows fast (vs. slow) dynamics, rapid decay (vs. maintainability), no imagery (vs. imagery), and (probably) automatic (vs. controlled) processing.     

Fast visual generation: Its nature and chronometrics

The fast-generation model for the matching of mixed-case letter pairs (e.g., Aa, Ab) states that one or both members of a pair activate visual representations in memory of the opposite case, supporting “same” or “different” responses through crossmatching to representations of the pair members themselves. Here the reaction time and error results of three experiments using simultaneous matches support a specific variant of the model in which generation proceeds from the uppercase letter. Furthermore, a manipulation of stimulus onset asynchrony in a fourth experiment using near-simultaneous matches indicates that fast generation produces a visual representation that occurs within 67 msec of initiation and that decays within 200 msec. A fifth experiment contrasts simultaneous and successive matches and in the case of successive matches finds evidence in support of a regeneration process acting after an initial decay. Models of mixed-case matching that are based on the phonetic representation of letter names, or on abstract-letter identities, completely fail to account for the results. Fast generation is distinguishable from slow generation in that it shows fast (vs. slow) dynamics, rapid decay (vs. maintainability), no imagery (vs. imagery), and (probably) automatic (vs. controlled) processing.     

Visual recognition as a function of stimulus offset asynchrony and duration

The stimuli consisted of two complementary dot patterns that formed a bigram when they were flashed simultaneously; impairment of letter recognition developed when one of the patterns was briefly extended beyond the termination of the other (stimulus offset asynchrony). However, if the ratio of stimulus offset asynchrony to bigram duration remained constant, the probability of a correct recognition response also remained constant as duration varied over a 50- to 100-msec interval. When percent stimulus asynchrony increased, the impairment increased. An interaction between bigram letter position and each of bigram duration and percent stimulus asynchrony was observed with recognition accuracy greater in general for the letter in the left half of the field.     

Inhibitory processes in auditory selective attention: Evidence of location-based and frequency-based inhibition of return

The possibility that there is an inhibitory component to auditory covert orienting was addressed. Each trial consisted of a cue followed by a target, and listeners were required to detect, localize, or identify the frequency of the target. At 150-msec stimulus onset asynchrony (SOA), performance was best when stimuli sounded from the same location or were of the same frequency. However, at 750-msec SOA, performance was best when stimuli differed in location or were of different frequencies. These results document the existence of both location-based and frequency-based auditory inhibition of return.     

The time course of visual influences in letter recognition

This study builds on a specific characteristic of letters of the Roman alphabet—namely, that each letter name is associated with two visual formats, corresponding to their uppercase and lowercase versions. Participants had to read aloud the names of single letters, and event-related potentials (ERPs) for six pairs of visually dissimilar upper- and lowercase letters were recorded. Assuming that the end product of processing is the same for upper- and lowercase letters sharing the same vocal response, ERPs were compared backward, starting from the onset of articulatory responses, and the first significant divergence was observed 120 ms before response onset. Given that naming responses were produced at around 414 ms, on average, these results suggest that letter processing is influenced by visual information until 294 ms after stimulus onset. This therefore provides new empirical evidence regarding the time course and interactive nature of visual letter perception processes.     

Effects of signal duration and masker duration on detectability under diotic and dichotic listening conditions

The detectability of a 500-Hz tone of either 32- or 256-msec duration in a broad-band 50-dB spectrum level noise was measured as a function of the duration of the noise. The noise was continuous or was gated 0, 125, or 250 msec before the onset of the signal. For the gated noise conditions the noise was terminated approximately 5 msec after termination of the signal. With a homophasic condition (NO SO), the three noise conditions led to approximately the same detectability as did the continuous masker. In an antiphasic condition (NO Sπ), detectability was poorest when signal and masker began together and improved as the delay between noise onset and signal onset increased. The difference between the simultaneous onset and the continuous noise condition was about 9 dB for the 32-msec signal and about 2 dB for the 256-msec signal. These results are compared to those reported by McFadden (1966).     

Semantic priming and retrieval from lexical memory: Evidence for facilitatory and inhibitory processes

Immediately prior to each visually presented target letter string to which the subject made a speeded word-nonword classification response, a visually presented prime to which no overt response was required was shown for 360, 600, or 2,000 msec. For word (W) target trials, the priming event was either a semantically neutral warning signal (Condition NX), a word semantically related to the target word (Condition R), or a word semantically unrelated to the target word (Condition U); for nonword (N) target trials, the priming event was either the neutral warning signal (Condition NX) or a word prime (Condition WP). For the W target trials, reaction times (RTs) were slower in Condition U than in Condition NX and equally so for all three prime durations; RTs were faster in Condition R than in Condition NX and to a greater degree for the 600- and 2,000-msec prime durations than for the 360-msec prime duration. For the N targets, RTs were faster in Condition WP than in Condition NX and equally so for all prime durations. These results were interpreted within the framework of a two-factor theory of attention proposed by Posner and Snyder (1975a).     

Letter-position coding in random consonant arrays

The processing of letter-position information in randomly arranged consonant strings was investigated using a masked prime variant of the alphabetic decision (letter/nonletter classification) task. In Experiment 1, primes were uppercase consonant trigrams (e.g., FMH) and targets were two uppercase Xs accompanied by the target letter or a nonletter (e.g., XMX, X%X). Response times were systematically faster when target letters were present in the prime string than when target letters were not present in the prime string. These constituent letter-priming effects were significantly stronger when the target letter appeared in the same position in the prime and target stimuli. This contrast between position-specific and position-independent priming was accentuated when subjects responded only when all the characters in the target string were letters (multiple alphabetic decision) in Experiments 2 and 3. In Experiment 4, when prime exposure duration was varied, it was found that position-specific priming develops earlier than position-independent priming. Finally, Experiment 5 ruled out a perceptual-matching interpretation of these results. An interpretation is offered in terms of position-specific and position-independent letter-detector units in an interactiveactivation framework.     

Parallel and competing operations in visual and memory search

Two adjacent probe letters exposed at variable asynchrony are searched for the presence of one target letter drawn from a set of one, three, or five memorized targets. Latency of decision was longer at 70-msec ISI than at 150, 300, and 500, except that at 300-msec ISI there was also an elevated response lateney to a target when it occurred as the first of two probes. Models of search through successive probes must be qualified to accommodate these divergences from monotonicity. Interference between near-simultaneous inputs may account for the longer lateney at 70-msee ISI, and competition for processing capacity by operations at different processing stages could be involved in the effeet at 300-msec ISI. 1972, Psychonomic Society, Inc., Austin, Texas     

A comparison of auditory and visual apparent motion presented individually and with crossmodal moving distractors

Unimodal auditory and visual apparent motion (AM) and bimodal audiovisual AM were investigated to determine the effects of crossmodal integration on motion perception and direction-of-motion discrimination in each modality. To determine the optimal stimulus onset asynchrony (SOA) ranges for motion perception and direction discrimination, we initially measured unimodal visual and auditory AMs using one of four durations (50, 100, 200, or 400 ms) and ten SOAs (40-450 ms). In the bimodal conditions, auditory and visual AM were measured in the presence of temporally synchronous, spatially displaced distractors that were either congruent (moving in the same direction) or conflicting (moving in the opposite direction) with respect to target motion. Participants reported whether continuous motion was perceived and its direction. With unimodal auditory and visual AM, motion perception was affected differently by stimulus duration and SOA in the two modalities, while the opposite was observed for direction of motion. In the bimodal audiovisual AM condition, discriminating the direction of motion was affected only in the case of an auditory target. The perceived direction of auditory but not visual AM was reduced to chance levels when the crossmodal distractor direction was conflicting. Conversely, motion perception was unaffected by the distractor direction and, in some cases, the mere presence of a distractor facilitated movement perception.     

Relationship between flanker identifiability and compatibility effect

What is the relation between the identifiability of masked flankers and their ability to induce compatibility effects in a letter classification task? Using a within-subjects design (n=8), we first determined identification performance for two flankers (H or N) around an irrelevant target letter as a function of the time (stimulus onset asynchrony, or SOA) after which the flankers were masked. In a second condition, subjects classified the central letter of the same stimulus patterns irrespectively of the identity of the flankers. The compatibility effects increased with increasing identification performance as a function of SOA, and we found a significant compatibility effect even at an SOA at which the identifiability of the flankers did not differ significantly from zero. We discuss the statistical power of our design and an interpretation of our results in terms of a dissociation between perceptual processes and processes directly activating the motor system (direct parameter specification; cf. Neumann, 1990).     

Priming of abstract letter representations may be universal: The case of Arabic

Recent research on the Roman alphabet has demonstrated that the magnitudes of masked repetition priming are equivalent for letter pairs that have similar visual features across cases (e.g., c-C) and for letter pairs with dissimilar features (e.g., g-G). Here, we examined whether priming of abstract letter representations occurs in an orthographic system, Arabic, in which the letters show an intricate number of contextual forms. Arabic does not have a lowercase/uppercase distinction, but the letters exhibit different forms that depend on their position (initial, medial, final, or isolated) and their connectivity. Importantly, some letters look quite different across positions (e.g., (symbol in text) and (symbol in text), which correspond to the letter 'ayn), whereas others look very similar (e.g. (symbol in text), and (symbol in text), which correspond to the letter fā'). We employed a masked priming same-different task, in which native speakers of Arabic decided whether a target letter was the same as or different from a reference letter presented in a different position (middle vs. isolated). The results showed masked repetition priming effects of the same magnitude for letter pairs with similar and with dissimilar visual features across letter positions. These data support the view that priming of abstract letter representations is a universal phenomenon.     

Saccade latency and warning signals: Stimulus onset,offset, and change as warning events

Two experiments investigated saccade latency to a peripheral target under various warning signal conditions. In Experiment I, the effects of warning stimulus onset, change, and two offset conditions were compared at warning intervals of 0, 100, 300, and 600 msec. Warning stimulus onset, change, and offset were all effective in reducing saccade latency as compared to a no-warning control condition, but warning stimulus offset resulted in shorter saccade latency than onset or change at all warning intervals. Experiment 2 compared onset and offset warning conditions at ?300-, ?250-, ?200-, ?150-, ?100-, ?50-, 0-, and 50-msec intervals. Responses following onset were slower than those following offset at the latter five intervals, while warning onset resulted in slower saccades than no-warning control conditions at ?150-, ?100-, and ?50-msec intervals. These results indicate that the onset of a visual warning signal can have an interfering effect on the programming or execution of a saccade.     

Strategic reliance on phonological mediation in lexical access

The present study investigated strategic variation in reliance on phonological mediation in visual word recognition. In Experiment 1, semantically related or unrelated word primes preceded word, pseudohomophone (e.g.,trane), or nonpseudohomophone (e.g.,trank) targets in a lexical decision task. Semantic priming effects were found for words, and response latencies to pseudohomophones were longer in related than in unrelated prime conditions. In Experiment 2, related or unrelated word primes preceded word or pseudohomophone targets. A relatedness effect was found for words, although it was significant at a 600-msec prime-target stimulus onset asynchrony (SOA) and not at a 200-msec SOA. There was no relatedness effect for pseudohomophones. Experiment 3 was a replication of Experiment 2, except that pseudohomophones were replaced by nonpseudohomophonic orthographic controls. Facilitation effects for related target words were greater in Experiment 3 than in Experiment 2. The results reflect apparent variations in the expectation that a related prime reliably indicates that a target is a word. Although reliance on phonological mediation might be strategically contingent, there could be a brief time period in which phonologically mediated lexical access occurs automatically. Whether phonological information is maintained or suppressed subsequently depends on its overall usefulness for the task.     

Top-down and bottom-up attentional control: on the nature of interference from a salient distractor.

In two experiments using spatial probes, we measured the temporal and spatial interactions between top-down control of attention and bottom-up interference from a salient distractor in visual search. The subjects searched for a square among circles, ignoring color. Probe response times showed that a color singleton distractor could draw attention to its location in the early stage of visual processing (before a 100-msec stimulus onset asynchrony [SOA]), but only when the color singleton distractor was located far from the target. Apparently the bottom-up activation of the singleton distractor's location is affected early on by local interactions with nearby stimulus locations. Moreover, probe results showed that a singleton distractor did not receive attention after extended practice. These results suggest that top-down control of attention is possible at an early stage of visual processing. In the long-SOA condition (150-msec SOA), spatial attention selected the target location over distractor locations, and this tendency occurred with or without extended practice.     

Top-down and bottom-up attentional control: On the nature of interference from a salient distractor

In two experiments using spatial probes, we measured the temporal and spatial interactions between top-down control of attention and bottom-up interference from a salient distractor in visual search. The subjects searched for a square among circles, ignoring color. Probe response times showed that a color singleton distractor could draw attention to its location in the early stage of visual processing (before a 100-msec stimulus onset asynchrony [SOA]), but only when the color singleton distractor was located far from the target. Apparently the bottom-up activation of the singleton distractor’s location is affected early on by local interactions with nearby stimulus locations. Moreover, probe results showed that a singleton distractor did not receive attention after extended practice. These results suggest that top-down control of attention is possible at an early stage of visual processing. In the long-SOA condition (150-msec SOA), spatial attention selected the target location over distractor locations, and this tendency occurred with or without extended practice.     

Facilitative and inhibitory effects of cuing sound duration, intensity, and timbre.

Two experiments are reported in which the possibility that auditory attention may be controlled in a stimulus-driven manner by duration, intensity, and timbre cues was examined. In both experiments, listeners were presented with a cue followed, after a variable time period of a 150-, 450-, or 750-msec stimulus onset asynchrony (SOA), by a target. In three different conditions for each experiment, the duration, intensity, or timbre relation between the cue and the target was varied so that, on 50% of the trials, the two sounds were identical and, on 50% of the trials, the two sounds were different in the manipulated feature. The two experiments differed only in the judgment required, with listeners in Experiment 1 identifying the duration, intensity, or timbre of the target and listeners in Experiment 2 indicating whether the target incorporated a brief silent gap. In both experiments, performance was observed to depend on both the similarity of and the time between the cue and the target. Specifically, whereas at the 150-msec SOA performance was best when the target was identical to the preceding cue, at the 750-msec SOA performance was best when the cue and the target differed. This pattern establishes the existence of duration-, intensity-, and timbre-based auditory inhibition of return. The theoretical implications of these results are considered.     

Facultative and inhibitory effects of location and frequency cues: Evidence of a modulation in perceptual sensitivity

The possibility that facilitative and inhibitory effects of auditory cues result because of a modulation in perceptual sensitivity was examined. Listeners were presented with a cue followed by a target, with the time period between the two varied at stimulus onset asynchronies (SOAs) of 150,450, or 750 msec. In two conditions, the cue and target were either the same or different in location or frequency. In both conditions, listeners were required to identify the rise time of the target. Whereas the cue was presented in isolation, the target was presented in a wide-band noise background such that the required discrimination was made relatively difficult. In both conditions, a facilitative effect was apparent at the 150-msec SOA and an inhibitory effect was apparent at the 750-msec SOA for both accuracy and response time measures of performance. That these results were apparent for a judgment unrelated to the manipulated cue-target relation suggests strongly that both location-based and frequency-based auditory inhibition of return result primarily because of changes in perceptual sensitivity.     

Facilitative and inhibitory effects of location and frequency cues: evidence of a modulation in perceptual sensitivity.

The possibility that facilitative and inhibitory effects of auditory cues result because of a modulation in perceptual sensitivity was examined. Listeners were presented with a cue followed by a target, with the time period between the two varied at stimulus onset asynchronies (SOAs) of 150, 450, or 750 msec. In two conditions, the cue and target were either the same or different in location or frequency. In both conditions, listeners were required to identify the rise time of the target. Whereas the cue was presented in isolation, the target was presented in a wide-band noise background such that the required discrimination was made relatively difficult. In both conditions, a facilitative effect was apparent at the 150-msec SOA and an inhibitory effect was apparent at the 750-msec SOA for both accuracy and response time measures of performance. That these results were apparent for a judgment unrelated to the manipulated cue-target relation suggests strongly that both location-based and frequency-based auditory inhibition of return result primarily because of changes in perceptual sensitivity.