Visual search for simple targets.

Quantitatively analyzed published data based on searching for simple targets (e.g., alphanumeric data, colors, and familiar shapes). Relationships were investigated for search time and scanning rate with the number of nontarget stimuli in an array, the number of possible targets, and the total amount of displayed information. On other grounds, a general relationship about time-controlled processes was postulated (i.e., that the rate of performance of a time-controlled process is an increasing function of the maximum stimulus, or information load, up to a limit). With this postulate, search performance (both as a function of the number of elements to be searched and the number of possible targets) can be accounted for in terms of a sequential information processing model. Results also suggest a maximum scanning capacity of 50 elements/sec, or 5.6 bits/sec of total information. Other factors suggested as important are the relative emphasis put on speed or accuracy; the dimensionality of the target (i.e., whether it differs from nontarget elements in 1 or more than 1 way); and the cognitive, or psychological, homogeneity of stimulus array. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perception of relational invariants by newborns.

Two studies investigated (1) the ability of 40 newborns (aged less than 1 wk) to detect relational invariants (Exp I) and (2) whether infants perceive stimulus elements as a single pattern of figures rather than as 2 discrete figures in relationship (Exp II). In Exp I, Ss were evaluated in a habituation-recovery paradigm for evidence of the ability to detect an invariant identity or nonidentity relationship between components of a visual stimulus. Ss who were initially habituated to stimuli consisting of 2 identical elements recovered fixation when the elements were rearranged to be dissimilar and vice versa. Control Ss who continued to see the familiarized stimuli at test yielded no recovery. To determine whether Ss might have perceived the stimulus elements as a single pattern of figures rather than as 2 discrete figures in relationship, a 2nd study was conducted in which circles that enclosed each element (and which were presumed to unitize each) were removed at test. Because Ss in this condition recovered responding at test, it was concluded that the circles had been visible in the 1st experiment and that the elements may thus have been perceived as discrete. Overall findings are consistent with the Gibsonian view that infants are inherently disposed to detect invariant, higher-order relational information (i.e., information that specifies significant objective properties of the environment). (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discrimination of relative numerosity and stimulus mixture by pigeons with comparable tasks.

Arrays of small squares of 2 colors were presented in various proportions to pigeons on a video screen. Birds pecked differentially at the left or right side of the screen to obtain grain. In Experiment 1, pecking at 1 side was correct when more blue than red elements were displayed; the other was correct with more red than blue. Proportions of responses to the 2 locations reflected the proportions of elements in an orderly manner and were little affected by alterations in spacing or size of elements. When red elements were replaced by green, the discrimination readily transferred to the new arrays. In Experiment 2, 1 side of the screen was correct when uniform red or blue arrays were presented; the other was correct for mixed arrays. Orderly gradients of response location reflected degree of stimulus mixture. Good transfer was obtained with green and blue elements. These results support the robust nature of discriminations of emergent properties of complex arrays when stimuli are equally associated with reinforcement and when response location, and not response rate, indicates stimulus control. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hippocampal lesions alter conditioning to conditional and contextual stimuli

The control of conditioned fear behaviour by a conditional stimulus (CS) and contextual stimuli (CXT) was compared in rats with lesions to the hippocampus (HPC) or neocortex (CO), and operated controls (OC). After classical fear conditioning in a distinctive context, rats were subsequently tested in the presence of the CS and CXT (CS + CXT), the CS alone (CS-only), or context alone (CXT-only). Two experiments were conducted in which conditioned fear was measured by an active avoidance response (experiment 1) or by response suppression (experiment 2). Groups did not differ in acquiring the conditioned fear response, as measured in the CS + CON test but, in both experiments, hippocampal (HPC) groups exhibited more conditioned fear behaviour than controls in the CXT-Only and CS-Only conditions. It was suggested that control rats conditioned the fear response to a stimulus complex that incorporated the CS and CTX. Rats with HPC lesions did not form this association between the stimulus elements; instead they segregated the CS and CXT and formed independent associations between the conditioned response (CR) and each component. In showing that HPC damage disrupts the process of forming associations between environmental stimuli and that the effect is not restricted to contextual cues, the results help to resolve apparently contradictory findings regarding the role of HPC in contextual information processing.     

Information theoretic analysis of dynamical encoding by filiform mechanoreceptors in the cricket cercal system

1. The stimulus/response properties of 20 mechanosensory receptors in the cricket cercal sensory system were studied using electrophysiological techniques. These receptors innervated filiform hairs of various lengths and directional selectivities. Previous studies have characterized the sensitivity of such cells to the direction of air currents and to the amplitude of sinusoidal stimuli. In the experiments reported here, the quantity and quality of information encoded in the receptors' elicited responses about the dynamics of more complex air current waveforms were characterized. 2. Based on a white analysis of receptor response properties, the median frequency of each receptor's frequency tuning curve was found to be strongly correlated with the length of its associated mechanosensory hair. The receptors connected to hairs > 900 microns encoded frequencies below approximately 150 Hz very accurately and the receptors connected to shorter hairs encoded progressively higher bands of frequencies. These results were interpreted within the constraints imposed by the biomechanics of the air current-to-cercus boundary. 3. The encoding accuracy was expressed in the information theoretic units of bits/second, which characterizes the information transmission rate of a receptor. The information rates of the neuronal spike trains ranged from 75 to 220 bits/s. The information transmission rate was not correlated with the length of the mechanosensory hair. The average amount of information transmitted per action potential was negatively correlated with receptor hair length and ranged between 0.6 and 3.1 bits/spike. Decoding of the receptor responses was restricted to linear transformations of the spike trains. 4. The stimulus/response latencies of the different receptors ranged between 5 and 11 ms, and the integration time of the receptors ranged between 8 and 30 ms. The latency of a receptor was only weakly correlated with the length of its associated hair, and a receptor's integration time was correlated with hair length. 5. The stimulus/response phase difference for receptor cells that innervated hairs longer than approximately 800 microns increased with frequency > 50 Hz. The phase responses for receptor cells connected to hairs < 800 microns did not vary for frequencies > 50 Hz.     

The Effects of Auditory and Visual Linguistic Distractors on Target Localization.

In this experiment, a Stroop-like paradigm was used to investigate the ability to attend to visuospatial cues while ignoring distracting stimuli in the auditory or visual modality. In Part 1, the authors investigated whether linguistic cue words (i.e., RIGHT, LEFT, DOWN, and UP) would induce endogenous shifts of attention to visual targets. In Part 2, a relevant distractor stimulus was introduced in a different modality from the endogenous cues to investigate effects of interference. Twenty-five right-handed students served as participants. Auditory and visual linguistic cues were effective in inducing shifts of visual attention when cues were presented alone. Furthermore, introducing a distractor stimulus decreased the efficacy of these cues differently depending on modality, suggesting that language processing and visuospatial attention may share neuronal resources. Implications for unimodal and supramodal mechanisms of selective attention and relevant neuronal networks are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Covert visual orienting across the lifespan.

Three groups of 20 K–5th graders, 20 college students, and 20 older adults (mean age 72.8 yrs) were tested. The S's task was the speeded discrimination of "X" from "O", but of primary interest was the effect of a location cue that appeared prior to the target. Both an abrupt stimulus cue and a voluntary information cue were studied using response time measures. Eye movements were monitored to control for differences in the ability to maintain fixation. Exp 1 showed that in comparison with young adults, children were less able to sustain orienting over time, and senior adults required more time to use the cue. Exp 2 (using K–1st graders, 4th–5th graders, 20 college students, and 20 older adults) tested the relation between stimulus and information cues when they both occurred prior to a given target. All age groups were able to use information cues in the presence of conflicting stimulus cues, but young adults were better able to do so than either children or senior adults. Results are interpreted as support for the view that separate mechanisms underlie stimulus-based versus information-based spatial orienting. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The cuing and priming of cognitive operations.

The effect on performance of advance information about the specific cognitive operations to be performed on a stimulus was investigated in two experiments using cues (information useful and necessary for performance) and primes (information useful but not necessary for performance). In the first experiment, a cue presented prior to a digit stimulus indicated whether the digit was to be classified as odd or even, or low (less than 6) or high (greater than 5). Results showed that performance improved with increasing time between cue and digit and with practice. A Stroop-like asymmetric interference of the low–high operation on the odd–even operation was also observed. In the second experiment, a prime that matched the cue, mismatched it, or was neutral was presented before the cue. Results showed facilitatory and inhibitory priming effects, as well as a distance effect based on the position of a digit relative to the boundary between 5 and 6. The results of both experiments were discussed in terms of a model based on relative processing speeds of the two relevant properties of the digits. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selective responding by autistic children to multiple sensory input.

Reinforced 6 autistic, 5 retarded, and 5 normal children for responding to a complex stimulus involving the simultaneous presentation of auditory, visual, and tactile cues. After discrimination was established, elements of the complex were presented separately to assess which aspects of the complex stimulus had acquired control over the S's behavior. It was found that (a) the autistics responded primarily to only 1 of the cues, normals to all 3 cues, and retardates to 2 cues; and (b) conditions could be arranged such that a cue which had remained nonfunctional when presented in association with other cues could be established as functional when trained separately. Data fail to support theories that any 1 sense modality is impaired in autistic children. When presented with a stimulus complex, autistic Ss' attention was overselective. Findings are related to the literature on selective attention. Since much learning involves contiguous or near-contiguous pairing of 2 or more stimuli, failure to respond to 1 of the stimuli may be an important factor in the development of autism. (27 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pavlovian conditioning of sexual arousal: Parametric and background manipulations.

Recent studies have shown that a Pavlovian conditioned stimulus (CS) for unconsummated sexual arousal can increase the rate of copulation in the rat. The present report includes 5 experiments examining the effects of parametric manipulations on the conditioned arousal response in 216 male and more than 136 ovariectomized female Long-Evans hooded rats. Results show that 6–9 trials are necessary for reliable conditioning, but extinction is somewhat slower than acquisition. The function for the CS/unconditioned stimulus (UCS) interval is quadratic, with a minimum of several minutes required for effective conditioning. In the 1st 3 experiments, it appeared that background cues were conditioned as well as the designated CSs, and this was tested explicitly in the last 2 studies. In one, the effect of background cues was shown by training and testing in different situations; in the 2nd, background cues were shown to be subject to latent inhibition. Results demonstrate the influence of Pavlovian learning in sexual behavior and help to provide the basis for an animal model of the acquisition of deviant sexual arousal in humans. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Numerical reproduction in pigeons.

Pigeons were trained to match the number of responses made during a production phase to the number of keylight flashes (2, 4, or 6) in a previous sample phase. In Experiment 1, there were 2 conditions in which the flashes were programmed to occur at a constant rate or within a constant overall duration. For both conditions, although accuracy was relatively low, responding increased linearly with flash number and coefficients of variation decreased. Positive transfer to novel numbers was obtained only when test and baseline trials had the same temporal organization, but multiple regressions revealed significant control by number independently of temporal cues. In Experiment 2, flashes were programmed to occur pseudorandomly to degrade the validity of temporal cues. Results were similar to in Experiment 1. A prototype response class model accounted for the major features of the data. According to the model, responses during the production phase are shaped into higher order units that are associated with different stimulus numbers and function as a rough category scale of numerosity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The generality of the effects of cue structure similarity on cue discrimination and recall.

Investigated the effect of cue similarity on associative learning, recall, and cue discrimination in 5 experiments involving a total of 634 undergraduates as Ss. In all experiments, cues consisted of 3 elements shared with other cues. Position and consistency of these elements varied among different conditions. In each experiment, Ss associated some kind of target information with a meaningless string of consonants or meaningful words. The procedures for acquisition included (1) single vs multiple study presentations, (2) a long mixed list containing various structures, (3) incidental learning involving semantic processing of cues and targets, (4) use of sentences containing both cues and targets, and (5) embedding cues and targets in a story. Results show that shared elements produced interference with all procedures and materials. (French abstract) (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pigeons learn stimulus identity and stimulus relations when both serve as redundant, relevant cues during same-different discrimination training.

The authors taught pigeons to discriminate displays of 16 identical items from displays of 16 nonidentical items. Unlike most same-different discrimination studies-where only stimulus relations could serve a discriminative function-both the identity of the items and the relations among the items were discriminative features of the displays. The pigeons learned about both stimulus identity and stimulus relations when these 2 sources of information served as redundant, relevant cues. In tests of associative competition, identity cues exerted greater stimulus control than relational cues. These results suggest that the pigeon can respond to both specific stimuli and general relations in the environment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Use of Visual, Acoustic, and Olfactory Information During Embedded Invertebrate Foraging in Brown Capuchins (Cebus apella).

Experiments were conducted to investigate which sensory cues are used by brown capuchins (Cebus apella) in embedded invertebrate foraging. The importance of visual, olfactory, and acoustic cues in such foraging was determined by presenting subjects with a stimulus log modified to block out given sensory cues. Experiment 1 was designed to investigate whether subjects could locate an invertebrate embedded in wood when only visual, acoustic, or olfactory information was available. Experiments 2 and 3 were designed to investigate extractive foraging behavior when two sensory cues were provided. It was hypothesized that the combination of visual and acoustic information would be necessary for subjects to successfully locate embedded invertebrates. Results indicated that subjects' performance was most successful when both visual and acoustic information was available. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus control after extradimensional training in pigeons: A comparison of response contingent and noncontingent training procedures.

In an experiment with a total of 32 White Carneaux pigeons, 2 groups of Ss for which reinforcement was procured by keypecking were given true discrimination (TD) or pseudodiscrimination (PD) training with different colors of the house light before they were taught to peck at a display of 3 vertical lines and tested on the line orientation continuum. 2 other groups were trained in the same way except that no response was required during discrimination training. Of the latter groups, the TD-trained Ss acquired the keypecking response (with autoshaping) more quickly than the PD-trained Ss. Their generalization gradients did not differ. Of the former groups, the TD-trained Ss produced a steeper generalization gradient than the PD-trained Ss. These results suggest that (a) general transfer effects are produced by TD and PD training and (b) differential stimulus control resulting from these procedures is mediated by the operation of response-produced cues. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of reward timing information on cue associability are mediated by amygdala central nucleus.

The central nucleus of the amygdala (CeA) has been implicated in a range of associative learning phenomena often attributed to changes in attentional processing of events. Experiments using a number of behavioral tasks have shown that rats with lesions of CeA fail to show the enhancements of stimulus associability that are normally induced by the surprising omission of expected events. By contrast, in other tasks, rats with lesions of CeA show normal enhancements of associability when events are presented unexpectedly. In this experiment, we examined the effects of CeA lesions on changes in cue associability in a reward timing task. In sham-lesioned rats, the associability of cues that were followed by stimuli that provided reward timing information was maintained at higher levels than that of cues that were followed by uninformative stimuli. Rats with lesions of CeA failed to show this advantage. These results indicate that the role of CeA in the modulation of associability is not limited to cases of event omission. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Size constancy in psychopathology.

Size-constancy judgments were made by 21 schizophrenics, 17 psychotically depressed, 16 hysterical character disordered patients, and 35 normal controls. Judgments were obtained for a neutral stimulus, a circle of light, under 4 experimental conditions which varied the number of distance cues available to S. The psychotic patients were more constant in all experimental conditions; all groups exhibited increasing constancy with increasing distance cues. Anchor effects were less for the controls and most marked in the schizophrenics and hysterical character disorders when distance cues were minimal. Results are interpreted as a function of an integrative defect in perception relating to psychosis rather than specific to schizophrenia. It is hypothesized that the psychotics are more sensitive to the information available whether or not such information leads to veridical perception. (16 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reaction of Escherichia coli cytochrome bo3 with substoichiometric ubiquinol-2: a freeze-quench electron paramagnetic resonance investigation

The reaction of the quinol oxidase cytochrome bo3 from Escherichia coli with ubiquinol-2 (UQ2H2) was carried out using substoichiometric (0.5 equiv) amounts of substrate. Reactions were monitored through the use of freeze-quench EPR spectroscopy. Under 1 atm of argon, semiquinone was formed at the QB site of the enzyme with a formation rate constant of 140 s-1; the QB semiquinone EPR signal decayed with a rate constant of about 5 s-1. Heme b and CuB were reduced within the 10-ms dead time of the freeze-quench experiment and remained at a constant level of reduction over the 1-s time course of the experiment. Quantitation of the reduction levels of QB and heme b during this reaction yielded a reduction potential of 30-60 mV for heme b. Under a dioxygen atmosphere, the rates of semiquinone formation and its subsequent decay were not altered significantly. However, accurate quantitation of the EPR signals for heme b and heme o3 could not be made, due to interference from dioxygen. In the reaction between the QB-depleted enzyme and UQ2H2 under substoichiometric conditions, there was no observable change in the EPR spectra of the enzyme over the time course of the reaction, suggesting an electron transfer from heme b to the binuclear site in the absence of QB which occurs within the dead time of the freeze-quench apparatus. Analysis of the thermodynamics and kinetics of electron transfers in this enzyme suggests that a Q-cycle mechanism for proton translocation is more likely than a cytochrome c oxidase-type ion-pump mechanism.     

Effects of cue context on the perception of depth from combined disparity and perspective cues

PURPOSE: In normal vision, stereoscopic cues are combined with perspective cues to provide veridical depth perception. The relative strengths of these depth cues, however, may be dependent upon context effects. We investigated the role of stimulus context on the interactions of binocular disparity, contrast, and size. METHODS: The subjects, four observers with normal stereoacuity and one stereo-amblyope, discriminated far vs. near perceived depth of Gabor patches; feedback was based on the sign of binocular disparity. Depth discrimination functions were measured under conditions in which depth cues were consonant or in conflict. Three stimulus contexts were used: (1) variable disparity with fixed spatial frequency and contrast; (2) variable contrast with fixed spatial frequency and disparity; and (3) variable spatial frequency with fixed contrast and disparity. The effects of stimulus context were derived from comparisons of discrimination rates for identical stimuli across the three sets of conditions. RESULTS: In subjects with normal stereopsis, for disparities less than 2 arcmin, depth perception was dominated by contrast in contrast-varying sessions, or by size in spatial frequency-varying sessions. With larger disparities, depth perception became dependent on disparity, regardless of the contrast or spatial frequency of the test stimulus. The results for the stereo-amblyope showed much greater dependence on perspective cues and, in most cases, the transition from perspective- to disparity-based depth perception did not occur. CONCLUSIONS: These investigations demonstrate strong stimulus context effects and have important implications for the combination rules of stereoscopic and perspective cues in depth perception of normal and stereo-deficient subjects.     

Enhanced rate of intramolecular electron transfer in an engineered purple CuA azurin

The recent expression of an azurin mutant where the blue type 1 copper site is replaced by the purple CuA site of Paracoccus denitrificans cytochrome c oxidase has yielded an optimal system for examining the unique electron mediation properties of the binuclear CuA center, because both type 1 and CuA centers are placed in the same location in the protein while all other structural elements remain the same. Long-range electron transfer is induced between the disulfide radical anion, produced pulse radiolytically, and the oxidized binuclear CuA center in the purple azurin mutant. The rate constant of this intramolecular process, kET = 650 +/- 60 s-1 at 298 K and pH 5.1, is almost 3-fold faster than for the same process in the wild-type single blue copper azurin from Pseudomonas aeruginosa (250 +/- 20 s-1), in spite of a smaller driving force (0.69 eV for purple CuA azurin vs. 0.76 eV for blue copper azurin). The reorganization energy of the CuA center is calculated to be 0.4 eV, which is only 50% of that found for the wild-type azurin. These results represent a direct comparison of electron transfer properties of the blue and purple CuA sites in the same protein framework and provide support for the notion that the binuclear purple CuA center is a more efficient electron transfer agent than the blue single copper center because reactivity of the former involves a lower reorganization energy.