Target Discrimination Task Research Articles

P3a from white noise

P3a and P3b event-related brain potentials (ERPs) were elicited with an auditory three-stimulus (target, distracter, and standard) discrimination task in which subjects responded only to the target. Distracter stimuli consisted of white noise or novel sounds with stimulus characteristics perceptually matched. Target/standard discrimination difficulty was manipulated by varying target/standard pitch differences to produce relatively easy, medium, and hard tasks. Error rate and response time increased with increases in task difficulty. P3a was larger for the white noise compared to novel sounds, maximum over the central/parietal recording sites, and did not differ in size across difficulty levels. P3b was unaffected by distracter type, decreased as task difficulty increased, and maximum over the parietal recording sites. The findings indicate that P3a from white noise is robust and should be useful for applied studies as it removes stimulus novelty variability. Theoretical perspectives are discussed.

How Prevalent Is Object-Based Attention?

Previous research suggests that visual attention can be allocated to locations in space (space-based attention) and to objects (object-based attention). The cueing effects associated with space-based attention tend to be large and are found consistently across experiments. Object-based attention effects, however, are small and found less consistently across experiments. In three experiments we address the possibility that variability in object-based attention effects across studies reflects low incidence of such effects at the level of individual subjects. Experiment 1 measured space-based and object-based cueing effects for horizontal and vertical rectangles in 60 subjects comparing commonly used target detection and discrimination tasks. In Experiment 2 we ran another 120 subjects in a target discrimination task in which rectangle orientation varied between subjects. Using parametric statistical methods, we found object-based effects only for horizontal rectangles. Bootstrapping methods were used to measure effects in individual subjects. Significant space-based cueing effects were found in nearly all subjects in both experiments, across tasks and rectangle orientations. However, only a small number of subjects exhibited significant object-based cueing effects. Experiment 3 measured only object-based attention effects using another common paradigm and again, using bootstrapping, we found only a small number of subjects that exhibited significant object-based cueing effects. Our results show that object-based effects are more prevalent for horizontal rectangles, which is in accordance with the theory that attention may be allocated more easily along the horizontal meridian. The fact that so few individuals exhibit a significant object-based cueing effect presumably is why previous studies of this effect might have yielded inconsistent results. The results from the current study highlight the importance of considering individual subject data in addition to commonly used statistical methods.

Automated Symbolic Orienting: The Missing Link

Attention can be controlled either exogenously, driven by the stimulus features, or endogenously, driven by the internal expectancies about events in the environment. Extending this prevailing framework, we (Ristic and Kingstone, 2012) recently demonstrated that performance could also be independently controlled by overlearned behaviorally relevant stimuli, like arrows, producing automated effects. Using a difficult target discrimination task within a double cuing paradigm, here we tested whether automated orienting engages selective attention, and if in doing so it draws on its own pool of attentional resources. Our data unequivocally support both possibilities, and indicate that human attention networks are uniquely specialized for processing behaviorally relevant information.

Object-based control of attention is sensitive to recent experience.

How is attention guided by past experience? In visual search, numerous studies have shown that recent trials influence responses to the current trial. Repeating features such as color, shape, or location of a target facilitates performance. Here we examine whether recent experience also modulates a more abstract dimension of attentional control, object-based and location-based control. Participants performed a cued target discrimination task with stimuli presented on 2 rectangles. Response times to targets appearing in an uncued location on a cued rectangle were faster than to targets on the uncued rectangle, demonstrating an object-based attentional benefit. We investigated the object-based benefit on the current trial contingent on the cue-target relationship on the previous trial. The object-based benefit was significant only when the cued object contained the target on the previous trial, not when the uncued object contained the target. This effect of recent experience was not due to either the repetition of spatial cue-target location or the repetition of the response, but to adaptation to contingencies in the environment. Our results suggest a unifying view of attentional control that spans the concrete dimensions of control (e.g., determining the relative importance of red vs. blue) to the abstract (determining the relative importance of objects vs. locations in space). Attention closely tracks the short time scale structure of the environment and automatically adapts to optimize performance to this structure.

Similarities in echolocation strategy and click characteristics between a Pseudorca crassidens and a Tursiops truncatus

A previous comparative analysis of normalized click amplitude spectra from a Tursiops truncatus has shown that those frequencies with the lowest click-to-click variability in spectral content were the frequencies the animal paid attention to during target discrimination tasks. In that case, the dolphin only paid attention to the frequency range between 29-42 kHz which had a significantly higher degree of consistency in spectral content than frequencies above 42 kHz. Here it is shown that despite their morphological and behavioral differences, this same pattern of consistency was used by a Pseudorca crassidens performing a similar discrimination task. This comparison between species provides a foundation for using spectral level variability to determine the frequencies most important for echolocation in rare species and non-captive animals. Such results provide key information for successful management.

Spatial orientation of different frequencies within the echolocation beam of a Tursiops truncatus and Pseudorca crassidens

A 2D array of hydrophones was created to determine the spatial distribution of frequencies within the echolocation beam of a Tursiops truncatus. This Tursiops was shown previously to only pay attention to frequencies between 29 and 42 kHz while echolocating. It was found that the 30 kHz frequency was tightly focused, and the spatial location of the focus was consistently pointed toward the target. At 50 kHz, there was less focusing and less precision in being pointed at the target. At 100 kHz, the focus was often completely lost and was not pointed at the target. This indicates that this dolphin was actively focusing the frequencies it paid attention to toward the target, while the frequencies not paid attention to were left unfocused and undirected. This focusing was probably achieved through morphological manipulations of the melon and nasal air sacs. This explains earlier observations of how the dolphin achieved consistent frequency content only in the 0–42 kHz range with simultaneous variability outside this range in echolocation clicks recorded with a single on-axis hydrophone. Similar results were observed for a Pseudorca crassidens, while performing similar target discrimination tasks. [Office of Naval Research Grant No 0014-08-1-1160 to P.E. Nachtigall supported this work.]

Emotional prosody rarely affects the spatial distribution of visual attention

Emotional manipulations have been demonstrated to produce leftward shifts in perceptual asymmetries. However, much of this research has used linguistic tasks to assess perceptual asymmetry and there are therefore two interpretations of the leftward shift. It may reflect a leftward shift in the spatial distribution of attention as a consequence of emotional activation of the right hemisphere; alternatively it may reflect emotional facilitation of right hemisphere linguistic processing. The current study used two non-linguistic attention tasks to determine whether emotional prosody influences the spatial distribution of visual attention. In a dual-task paradigm participants listened to semantically neutral sentences in neutral, happy or sad prosodies while completing a target discrimination task (Experiment 1) and a target detection task (Experiments 2 and 3). There was only one condition in one experiment that induced perceptual asymmetries that interacted with emotional prosody, suggesting that task-irrelevant emotional prosody only rarely directs attention. Instead a more likely cause of the leftward perceptual shift for comprehension of emotional speech is facilitation of right hemisphere linguistic processing.

Size matters in object-based attentional selection

Stimuli We manipulated object width in a visual target discrimination task similar to that of Egly et al.1. Subjects were presented with two parallel rectangles or two trapezoids, with both objects presented vertically or horizontally. Rectangles were identical and of two possible widths ('narrow' or 'large'). Trapezoids were identical but in opposite orientations, with the 'narrow' base of one object adjacent to the 'large' base of the other. Results

The effect of smoking on sensory and attentional masking

This study examined the influence of smoking on low-level sensory and higher level visual cognitive abilities. Three groups (nonsmokers, deprived smokers, and nondeprived smokers) of 22 observers were tested using a visual target discrimination task. To assess sensory and visual cognitive differences, a masking task developed by Enns and Di Lollo (1997) was used. In the task, the target was masked by either a contour mask (contour masking) or an object mask (attentional masking by object substitution). The strongest masking effects were found in the group of nondeprived smokers, for both sensory and attentional masking. This pattern of results as well as results in the deprived smokers indicated changes in transient visual processing channels due to the acute actions of nicotine, not mediated by withdrawal relief.

Feature extraction and classification of metal detector signals using the wavelet transform and the fuzzy ARTMAP neural network

In this paper, the Fuzzy ARTMAP (FAM) neural network is used to classify metal detector signals into different categories for automated target discrimination. Feature extraction of the metal detector signals is conducted using a wavelet transform technique. The FAM neural network is then employed to classify the extracted features into different target groups. A series of experiments using individual FAM networks and a voting FAM network is conducted. Promising classification accuracy rates are obtained from using individual and voting FAM networks, respectively. The experimental outcomes positively demonstrate the effectiveness of the generated features, and of the FAM network in classifying metal detector signals for automated target discrimination tasks.

Constraints on task-based control of behaviour following frontal lobe damage: A single-case study

What factors determine stimulus-driven responses in patients with utilization behaviour? We examined this question by assessing the influence of an irrelevant cue on visual search in a patient showing evidence of utilization behaviour (F.K.), following bilateral damage to the medial frontal and temporal lobes. Despite being able to repeat the instructions, F.K. often responded to an item in the search display that matched the cue rather than the target. This effect was reduced under certain conditions: (a) when the cue–search interval increased, (b) when F.K. paid less attention to the cue, and (c) when the target discrimination task was made more difficult. On the other hand, the effect arose even when the cue was always invalid. We suggest that information from the cue competed with the top-down set to determine search. F.K.'s lesion makes it difficult for him to impose top-down knowledge rapidly, leading to responses automatically being based on attended, but irrelevant, cues under short cue–display intervals.

Functional bandwidth of an echolocating Atlantic bottlenose dolphin (Tursiops truncatus)

The frequency band that an Atlantic bottlenose dolphin (Tursiops truncatus) used to perform an echolocation target discrimination task was determined using computer simulated phantom targets. The dolphin was trained to discriminate frequency filtered phantom targets from unfiltered ones in a go/no-go paradigm. The dolphin's performance indicated perception of echo alteration only when applied filters interfered with the frequency band between 29 and 42 kHz. The dolphin did not behaviorally convey perception of applied filters that affected frequencies outside this functional bandwidth, such as a low pass 43 kHz or a high pass 28 kHz filter. The upper limit of the functional bandwidth at 42 kHz corresponded with the dolphin's upper hearing limit of 45 kHz, as determined through auditory evoked potential measurements. The lower limit of the functional bandwidth corresponded to a drop in intensity below 30 kHz within the dolphin's echolocation clicks. The randomized presentation of different filters showed that the dolphin paid attention to the entire 29-42 kHz band for each trial, not just subsets. The absence of temporal cues between some of the targets the dolphin could discriminate indicated that in these cases the target discrimination cues were based solely on the frequency content.

Recreational use of cocaine eliminates inhibition of return.

Chronic and recreational use of cocaine has been shown to impair inhibitory output control (response inhibition) but whether input control is also affected is an open question. For the first time, this study compared the ability to perform a cued target-discrimination task that measured inhibition of return (IOR), a reflexive inhibitory mechanism that delays attention from returning to a previously attended location, in adult recreational users and in a cocaine-free-matched sample controlled for age, race, gender distribution, and level of intelligence. Results show that the recreational use of cocaine eliminates IOR, suggesting that input control is strongly impaired.

Biomedical imaging for the study of auditory processes in the bottlenose dolphin.

The use of medical imaging techniques in marine mammalogy has traditionally consisted of anatomical investigations within postmortem specimens. Within the last decade, Ridgway pioneered the use of in vivo scanning techniques to study physiological processes in the bottlenose dolphin. His work utilizing PET and SPECT imagings to study processes that occur during half-brain sleep and long-term persistent vigilance have opened avenues for marine mammal research not previously realized. Leveraging off of the successes of Ridgway, new work on the processing of auditory signals in the dolphin brain is underway. A dolphin is trained to perform an echolocation task while out of water. Echolocation clicks are captured at the melon surface with a suction-cup embedded hydrophone and synthetic target echoes are returned to the dolphin via a jawphone attached to the pan of the lower jaw. Under this paradigm, the dolphin performs a target discrimination task while positioned in a PET scanner. Injection of radiotracers at the time of the discrimination task will be used to map regions of blood flow and/or metabolic activity during the task. Results will provide the first visualization of regional physiological processes associated with the processing of echoic information in the dolphin brain.

The selective processing of emotional visual stimuli while detecting auditory targets: An ERP analysis

Event-related potential studies revealed an early posterior negativity (EPN) for emotional compared to neutral pictures. Exploring the emotion–attention relationship, a previous study observed that a primary visual discrimination task interfered with the emotional modulation of the EPN component. To specify the locus of interference, the present study assessed the fate of selective visual emotion processing while attention is directed towards the auditory modality. While simply viewing a rapid and continuous stream of pleasant, neutral, and unpleasant pictures in one experimental condition, processing demands of a concurrent auditory target discrimination task were systematically varied in three further experimental conditions. Participants successfully performed the auditory task as revealed by behavioral performance and selected event-related potential components. Replicating previous results, emotional pictures were associated with a larger posterior negativity compared to neutral pictures. Of main interest, increasing demands of the auditory task did not modulate the selective processing of emotional visual stimuli. With regard to the locus of interference, selective emotion processing as indexed by the EPN does not seem to reflect shared processing resources of visual and auditory modality.

Effects of the cholinergic agonist nicotine on reorienting of visual spatial attention and top-down attentional control

The cholinergic agonist nicotine facilitates detection of invalidly cued trials in location-cueing paradigms and reduces the associated neural activity in human inferior parietal cortex. By using functional magnetic resonance imaging we test the hypothesis that the nicotinic modulation of attentional reorienting may result from reduced use of top-down information derived from prior cues. In a within subjects design non-smoking volunteers were given either placebo or nicotine (Nicorette® 2 mg gum) prior to performing a cued target discrimination task. Attention was either validly (80%) or invalidly (20%) cued to the right or left visual hemifield. The difference in reaction times to invalidly and validly cued targets is termed the ‘validity effect’ and indicates the costs for attentional reorienting. Nicotine reduced the validity effect and reorienting-related neural activity in right inferior parietal cortex. Further regions consistently modulated in their activity by nicotine were the right middle temporal gyrus, left middle frontal gyrus, left parahippocampal gyrus and right cerebellum. The effects of nicotine upon top-down modulation were investigated by comparing occipital activity when attending to the right vs. left visual hemifield under placebo and nicotine. If nicotine reduced the use of top-down information attentional modulation in occipital cortex should be smaller under nicotine as compared with placebo. Even though an attention-related modulation of neural activity was observed in the fusiform and middle occipital gyrus we found no evidence for differences in attentional modulation under placebo and nicotine. Our data support a role of nicotinic cholinergic receptors in facilitating several subcomponents of attentional reorienting via modulation of right inferior parietal, temporal and frontal brain activity. In contrast, the findings in the occipital cortex do not support the hypothesis that the effects of nicotine on attentional reorienting are due to reduced reliance on top-down information derived from prior cues.

Gamma oscillations in gerbil auditory cortex during a target-discrimination task reflect matches with short-term memory

Tightly stimulus-locked “evoked” and not tightly stimulus-locked “induced” gamma-band oscillations have been implicated in a variety of cognitive functions as well as more basic stimulus-related aspects of neuronal activity. The present study aimed at dissociating both aspects using a preparation in rodents trained to perform in a target-discrimination task while recording the intracerebral electrocorticogram in parallel from left and right auditory cortex. While stimulus-related aspects of gamma-band activity were already evident in the naïve subjects, aspects related to successful target-discrimination only emerged with learning. Frequency-modulated tones were employed as stimuli and were varied with respect to two stimulus dimensions, viz. “spectral content” and “modulation direction”. A target stimulus had to be discriminated in a GO/(NO-GO) paradigm from three non-target stimuli matching the target in only one or none of these dimensions. Analysis of the event-related potentials indicated that the physical stimulus parameters explained most of the variance in amplitude of most event-related potential components. For the evoked gamma-band activity no learning related modulations were found. The induced gamma-band activity showed a relationship with the similarity of a stimulus with the target that was most prominent in the right hemisphere. The correspondence between task-specific behavior and the amplitude of induced gamma-band activity, both developing with learning, supports a functional relevance of this form of oscillation beyond merely processing physical stimulus attributes.

Elemental associability changes in human discrimination learning.

Participants initially completed a discrimination task (D1) involving categorization of patterns with multiple common features, each feature being partly predictive of the correct response. In a subsequent target discrimination task (D2), these features were redistributed across new discriminative stimuli. The relative predictiveness of the features in D1 was either maintained in D2 (i.e., features were equally informative in D1 and D2) or switched (i.e., more informative features in D1 were made less informative in D2, and vice versa). Differential performance on D2 suggested that features most predictive of the correct D1 responses became more highly associable than features that were less predictive in D1. This finding suggests that the associability of individual stimulus elements changes as a consequence of their role in discrimination learning.

Elemental associability changes in human discrimination learning.

Participants initially completed a discrimination task (D1) involving categorization of patterns with multiple common features, each feature being partly predictive of the correct response. In a subsequent target discrimination task (D2), these features were redistributed across new discriminative stimuli. The relative predictiveness of the features in D1 was either maintained in D2 (i.e., features were equally informative in D1 and D2) or switched (i.e., more informative features in D1 were made less informative in D2, and vice versa). Differential performance on D2 suggested that features most predictive of the correct D1 responses became more highly associable than features that were less predictive in D1. This finding suggests that the associability of individual stimulus elements changes as a consequence of their role in discrimination learning.

Competition between simultaneous stimuli modulated by location probability in hemispatial neglect

Many aspects of spatial neglect can be explained as arising from competition for attentional selection, with salient ipsilesional stimuli emerging as the winner more often than contralesional stimuli. The outcome of the competition, however, can be affected both by bottom-up perceptual factors such as the gestalt properties of the display and by top-down factors such as expectancy or stimulus blocking. This study examines whether the competition for attentional selection can be modulated by manipulating the probability of the target's location in hemispatial neglect. Five patients with left-sided hemispatial neglect and a group of control participants performed a visual target discrimination task. In equal probability blocks, the target appeared randomly in any of six possible horizontal locations (three left, three right) whereas in biased blocks, the target appeared in the mid-location on the left on 50% of the trials and in each of the other locations on 10% of the trials. The target appeared either alone or was accompanied by a distractor on the opposite side. The results showed that the spatial bias facilitated detection of all left-sided targets in the neglect group, but was more spatially specific in the control group. Furthermore, while distractors on either side interfered with target processing in both groups, the patterns differed across the visual field. Finally, the magnitude of facilitation due to the bias was greatest in the condition with the most inhibition, i.e. a left-sided target accompanied by a right-sided distractor in the neglect group. These data underscore the competitive push–pull relationship between different bottom-up and top-down attentional factors, particularly within neglect patients, in whom a strong ipsilesional attentional bias already exists.