Automatic attention lateral asymmetry in visual discrimination tasks

There is evidence that automatic visual attention favors the right side. This study investigated whether this lateral asymmetry interacts with the right hemisphere dominance for visual location processing and left hemisphere dominance for visual shape processing. Volunteers were tested in a location discrimination task and a shape discrimination task. The target stimuli (S2) could occur in the left or right hemifield. They were preceded by an ipsilateral, contralateral or bilateral prime stimulus (S1). The attentional effect produced by the right S1 was larger than that produced by the left S1. This lateral asymmetry was similar between the two tasks suggesting that the hemispheric asymmetries of visual mechanisms do not contribute to it. The finding that it was basically due to a longer reaction time to the left S2 than to the right S2 for the contralateral S1 condition suggests that the inhibitory component of attention is laterally asymmetric.     

The elusive tradeoff: Speed vs accuracy in visual discrimination tasks

Theoretical models for choice reaction time and discrimination under time pressure must account for Ss’ ability to trade accuracy for increased speed. The fast guess model views these tradeoffs as different mixtures of “all-or-none” strategies, while incremental models assume they reflect different degrees of thoroughness in processing the stimulus. Three experiments sought tradeoffs for difficult visual discriminations, using explicit payoffs to control and manipulate pressures for speed and accuracy. Although guessing was pervasive, the simple fast guess model could be rejected; Experiments II and III obtained tradeoffs even when fast guesses were purged from Ss’ data. Tradeoff functions fit by several formulations revealed: (1) slower rates of increase in accuracy for more similar stimuli, and (2) substantial “dead times” (80–100 msec slower than detection times) before discrimination responses could exceed chance accuracy. Errors were sometimes faster and sometimes slower than correct responses (depending on S’s speed-accuracy trade); the latter effect may reflect a ceiling on S’s achievable accuracy. A final discussion examines implications of the results for models of discrimination under time pressure; it suggests modifications in present models, focusing on the random walk model, and describes an alternative “deadline” model.     

Good continuation affects discrimination of visual pattern information in young infants

A familiarization-novelty preference procedure was used to determine whether 3- to 4-month-old and 6- to 7-month-old infants utilize the Gestalt principle of good continuation to organize visual patterns. The study involved presentation of a target item (i.e., a square or diamond) either in-line or off-line with a set of distractor items (i.e., circles). Infants in both age groups responded to a change in the target element in the off-line, but not in the in-line, condition. The results suggest that infants organize visual pattern information in accord with the principle of good continuation. Implications of this finding for models of the ontogenesis and microgenesis of object perception in infants and adults are discussed.     

Impaired discrimination learning in mice lacking the NMDA receptor NR2A subunit

N-Methyl-D-aspartate receptors (NMDARs) mediate certain forms of synaptic plasticity and learning. We used a touchscreen system to assess NR2A subunit knockout mice (KO) for (1) pairwise visual discrimination and reversal learning and (2) acquisition and extinction of an instrumental response requiring no pairwise discrimination. NR2A KO mice exhibited significantly retarded discrimination learning. Performance on reversal was impaired in NR2A KO mice during the learning phase of the task; with no evidence of heightened perseverative responses. Acquisition and extinction of an instrumental behavior requiring no pairwise discrimination was normal in NR2A KO mice. The present findings demonstrate a significant and selective deficit in discrimination learning following loss of NR2A.     

Inhibition of return in discrimination tasks

Although inhibition of return is known to affect a wide range of detection tasks, it has not been found consistently in discrimination tasks. To examine this issue, 5 experiments were conducted in which participants discriminated between a visual target and a distractor. The responses were not inhibited if, before the onset of stimuli, attention had been overtly oriented (i.e., an eye movement was made) to the future target location and the stimulus at that location was the same symbol as the upcoming target. However, if attention was covertly oriented (i.e., no eye movement was made) to the future location of the target, or if the stimulus at the earlier attended location was a symbol different from the target, responses to the target were inhibited. Overall, the findings provide insights into the relation between movements of attention and discrimination judgments and support the notion that inhibition of return is an attentional phenomenon.     

Individual differences in visual discrimination of letters.

Research on the distinctive features of letters has been inconclusive. Investigators may have overlooked individual variations in their data which would have supported feature-extraction hypotheses but were concealed by analyses which averaged data into group means. Response latencies from a matching discrimination task with the 26 English capital letters were analyzed with INDSCAL, a multidimensional scaling procedure which weights individual contributions to a psychological space. Underlying a dimensions were linearity, curvature, angularity, and closure. The solution disclosed that individuals utilized these features differentially in the visual discriminations. The results suggest that future research in visual feature extraction will benefit from the examination of individual variations in the perceptual process.     

Transfer of directed-forgetting cues across discrimination tasks with pigeons

Directed forgetting is shown as impaired performance on a memory test following an instruction that the presented items will not be tested. Experiments utilizing the delayed matching-to-sample (DMTS) task have demonstrated that this ability to actively control memory is present in animals; however, no study has yet confirmed that cues to forget established in one DMTS discrimination will successfully transfer to other discriminations. Lacking such evidence, it is not clear whether forgetting cues act as “higher level” task instructions or are represented more simply, perhaps as part of a sample-specific sequence of events. The present study revealed good transfer of the forget cue function in pigeons after prior training with the forget cues in a separate discrimination. This finding is discussed in relation to analogous experiments on occasion setting, in which training within more than one discriminative context has been shown to be critical to the transfer of a conditional relation.     

Familiarity affects visual processing of words.

While previous research has demonstrated that words can be processed more rapidly and/or more accurately than random strings of letters, it has not been convincingly demonstrated that the superior processing of words is a visual effect. In the present experiment, the cases of letters were manipulated in letter strings that were to be compared on the basis of physical identity. Mean response time was shorter for words than for nonwords even for pairs of letter strings that differed only in case (e.g., site-site). This finding implies that the advantage of words over nonwords (the familiarity effect) typically observed in the simultaneous matching task is not due solely to comparison of either the word names or the letter names and, thus, that at least part of the familiarity effect must be due to more rapid formation and/or comparison of visual representations of the two letter strings when they are words. Further analysis failed to reveal a significant involvement of phonemic or lexical codes in the comparison judgments.     

Intrusion patterns in rapid serial visual presentation tasks with two response dimensions.

A rapid serial visual presentation (RSVP) paradigm using both one and two response dimensions was used to test parallel processing models of stimulus dimensions. Fifty subjects were asked to report the identity and/or color of a target uppercase word inserted in a series of lowercase words. The results produced a predominance of posttarget intrusions for color responses and a predominance of pretarget intrusions for identity responses. The requirement of a response to a second dimension impaired hit rates but did not change the pattern of intrusions. An examination of the distributions of intrusions in each response dimension as a function of the response given to the other dimension showed an unexpectedly high percentage of simultaneous hits, a moderate covariation between both responses, and the same patterns of intrusions when compared with the general distributions. While these results seem to be compatible with parallel models of processing for stimulus dimensions, two modifications to this model are suggested. First, the processing of response dimension(s) needs some attentional resources. Second, provision for a mixed model is indicated, which would include trials where no illusory conjunctions are formed.     

Differentiation of fluid, visual, and simultaneous cognitive tasks

The constructs of fluid reasoning and spatial visualization (Horn, 1989) as well as the construct of simultaneous processing (Luria, 1966) have been tapped by various cognitive assessment batteries. In order to determine whether these constructs could be differentiated from one another, factor analyses of subtest scores from six cognitive tasks were conducted. Fluid reasoning, spatial visualization, and simultaneous processing emerged as separate factors in the analysis, supporting the hypothesis that these constructs can be differentiated in psychoeducational testing. These results extend the findings of a preliminary study which found factorial differentiation between fluid and simultaneous reasoning.     

Simple and conditional visual discrimination with wheel running as reinforcement in rats.

Three experiments explored whether access to wheel running is sufficient as reinforcement to establish and maintain simple and conditional visual discriminations in nondeprived rats. In Experiment 1, 2 rats learned to press a lit key to produce access to running; responding was virtually absent when the key was dark, but latencies to respond were longer than for customary food and water reinforcers. Increases in the intertrial interval did not improve the discrimination performance. In Experiment 2, 3 rats acquired a go-left/go-right discrimination with a trial-initiating response and reached an accuracy that exceeded 80%; when two keys showed a steady light, pressing the left key produced access to running whereas pressing the right key produced access to running when both keys showed blinking light. Latencies to respond to the lights shortened when the trial-initiation response was introduced and became much shorter than in Experiment 1. In Experiment 3, 1 rat acquired a conditional discrimination task (matching to sample) with steady versus blinking lights at an accuracy exceeding 80%. A trial-initiation response allowed self-paced trials as in Experiment 2. When the rat was exposed to the task for 19 successive 24-hr periods with access to food and water, the discrimination performance settled in a typical circadian pattern and peak accuracy exceeded 90%. When the trial-initiation response was under extinction, without access to running, the circadian activity pattern determined the time of spontaneous recovery. The experiments demonstrate that wheel-running reinforcement can be used to establish and maintain simple and conditional visual discriminations in nondeprived rats.     

Repetition proportion affects masked priming in nonspeeded tasks

Masked repetition priming is often greater when a larger proportion of trials involve repetition primes, suggesting that a context-sensitive unconscious process may be operating. Two recent studies have failed to obtain an effect of prime proportion in the perceptual identification (PI) task, suggesting that the effect may not occur in nonspeeded tasks. Contrary to this possibility, we report proportion effects with masked repetition primes in two nonspeeded tasks: PI and fragment completion (FC). A proportion effect occurred in the accuracy measure only in the FC task, but it occurred in the reaction time measure in both tasks. Prior failures to find proportion effects in the PI task thus may have been due, in part, to the dependent measure used. We interpret our findings in light of several recent accounts of prime proportion effects with brief primes.     

The pigeon's variability discrimination with lists of successively presented visual stimuli.

Pigeons previously trained to peck 1 button (same) after the successive presentation of 16 identical pictures and to peck a 2nd button (different) after the successive presentation of 16 nonidentical pictures were tested on lists involving different degrees of variability, different list lengths, and different temporal organizations of list items. The pigeons' performances on this successive same-different task revealed a strong sensitivity to list entropy; but, their discrimination was also affected by their memory for list items and by the accumulated evidence for a same versus a different response. Statistical models confirmed and quantified the importance of these additional factors.     

Simultaneous visual discrimination in Asian elephants

Two experiments explored the behavior of 20 Asian elephants (Elephas aximus) in simultaneous visual discrimination tasks. In Experiment 1, 7 Burmese logging elephants acquired a white+/black- discrimination, reaching criterion in a mean of 2.6 sessions and 117 discrete trials, whereas 4 elephants acquired a black+/white- discrimination in 5.3 sessions and 293 trials. One elephant failed to reach criterion in the white+/black- task in 9 sessions and 549 trials, and 2 elephants failed to reach criterion in the black+/white- task in 9 sessions and 452 trials. In Experiment 2, 3 elephants learned a large/small transposition problem, reaching criterion within a mean of 1.7 sessions and 58 trials. Four elephants failed to reach criterion in 4.8 sessions and 193 trials. Data from both the black/white and large/small discriminations showed a surprising age effect, suggesting that elephants beyond the age of 20 to 30 years either may be unable to acquire these visual discriminations or may require an inordinate number of trials to do so. Overall, our results cannot be readily reconciled with the widespread view that elephants possess exceptional intelligence.     

Teaching coin discrimination to children with visual impairments

We taught 2 children with visual impairments to select a coin from an array using tactile cues after hearing its name and then to select a coin after hearing its value. Following the acquisition of these listener (receptive language) skills, we then observed the emergence of speaker (expressive language) skills without direct instruction.     

Size invariance in visual number discrimination

Summary This study deals with the observer's ability to discriminate the numerosity of two random dot-patterns irrespective of their relative size. One of these two patterns was a reference one that was always composed of 32 dots randomly distributed within aK ×K invisible square window (K = 1.92°). The second one was the test pattern with one of the five magnifications (K = 0.64°, 1.28°, 1.92°, 2.56°, 3.20°) and the relative number of dots varied on 11 levels (N = –15, –12, –9, –6, –3, 0, 3, 6, 9, 12, or 15 dots). The observer's task was to indicate which of the two patterns contained more dots. The results show that the stimulus size, as an irrelevant stimulus attribute, can be ignored in the judgements about relative numerosity. This means that the perceived numerosity is size invariant, at least for a 1.6-times magnification and a 3-times reduction of the test pattern. The size invariance observed constrains the range of potential models, since the perceived numerosity can be identified only by means of a feature of the stimulus that will remain invariant after any change in the absolute stimulus size.