Speeded Discrimination Task Research Articles

Speeded classification in simultaneous masking.

In simultaneous masking, flanking elements impair performance on a visual target. Previous studies on simultaneous masking have predominantly used discrimination threshold estimation to quantify performance on the target. Results based on thresholds suggest that an important factor in simultaneous masking is the strength of grouping between the target and the flankers. Recently Panis and Hermens (2014) showed that error rates in a speeded discrimination task, using the same simultaneous masking paradigm, provide a very similar pattern of results compared to thresholds from previous studies. In contrast, response times were found to deviate from the pattern in the error rates in some of the conditions, possibly providing a method to tap into low-level visual processes within the same paradigm. However, only a small number of masks was used, and it is therefore unclear to what extent differences can be found between thresholds, error rates, and response times. Here, we address this issue by examining speeded classification performance on a vernier target for a broad range of simultaneous mask layouts. Results suggest that thresholds and error rates are strongly associated, and that response times generally show the same pattern of results, although to a slightly weaker extent. We suggest that masking strength, defined by either measure, appears to be linked to target-flanker grouping rather than to low-level interactions.

Visual symmetry in objects and gaps

It is known that perceptual organization modulates the salience of visual symmetry. Reflectional symmetry is more quickly detected when it is a property of a single object than when it is formed by a gap between two objects. Translational symmetry shows the reverse effect, being more quickly detected when it is a gap between objects. We investigated the neural correlates of this interaction. Electroencephalographic data was recorded from 40 participants who were presented with reflected and translated contours in one- or two-object displays. Half of the participants discriminated regularity, half distinguished number of objects. An event-related potential known as the Sustained Posterior Negativity (SPN) distinguished between reflection and translation. A similar ERP distinguished between one and two object presentations, but these waves summed with the SPN, rather than altering it. All stimuli produced desynchronization of 8-13 Hz alpha oscillations over the bilateral parietal cortex. In the Discriminate Regularity group, this effect was right lateralized. The SPN and alpha desynchronization index different stages of visual symmetry discrimination. However, neither component displayed the Regularity × Objecthood interaction that is observed in speeded discrimination tasks, suggesting that integration of visual regularity with objectness is not inevitable. Instead, both attributes may be processed in parallel and independently.

Audiovisual Temporal Integration of Speech and Gesture

The relation between speech and gestures is a topic of vigorous research in language comprehension and production. Recent studies indicate that speech and gestures are integrated in language comprehension (Kelly, Özyürek, & Maris, 2010) with mutual and obligatory interactions (Kita & Özyürek, 2003). This hypothesis is also supported by neurophysiological findings on the integration of speech and gestures (Willems, Özyürek, & Hagoort, 2007). In the present study, using two behavioral tasks, we further investigated the integration of speech and gesture by focusing on the ‘unity effect’ (the perception of two or more sensory signals with spatiotemporal contiguity and semantic/informational relatedness is unified into a multisensory whole; e.g., Vatakis & Spence, 2007) from the multisensory literature. In particular, we manipulated the levels of semantic relatedness between speech and gestures. In Experiment 1, we presented a series of dynamic iconic gestures (i.e., “cut”, “saw”, “write”) with the respective auditory speech. We manipulated semantic congruency through three conditions: congruent, weakly incongruent (e.g., “cut” with “saw”), and strongly incongruent (e.g., “cut” or “saw” with “write”). Participants performed a speeded discrimination task of unimodal (audio or visual) and multimodal conditions by detection of two target gestures (e.g., respond when you see, hear, or both “cut” and “saw”; all stimulus combinations where tested in a blocked format). Analysis of the reaction times (RTs) revealed shorter RTs, as expected, for the multimodal congruent cases as compared to the unimodal and incongruent conditions presented. In Experiment 2, participants performed an unspeeded temporal order judgment task (TOJ). For the TOJ task the above mentioned conditions were presented with a set of stimulus onset ansynchronies (±541, ±333, ±208, ±125, and 0ms). Analysis of the just noticeable difference (JND) showed higher JNDs and, thus, worse performance for the congruent as compared to the incongruent condition. Both experiments, therefore, confirmed, for the first time, the unity effect in speech-gesture pairings, as well as the facilitation effect of semantic relatedness on the integration of speech and gestures. Overall, the present study confirms the hypothesis of integration between speech and iconic gestures, opening new pathways to research on multisensory and temporal relationships between the two communicative signals.

Endogenous Attention Signals Evoked by Threshold Contrast Detection in Human Superior Colliculus

Human superior colliculus (SC) responds in a retinotopically selective manner when attention is deployed on a high-contrast visual stimulus using a discrimination task. To further elucidate the role of SC in endogenous visual attention, high-resolution fMRI was used to demonstrate that SC also exhibits a retinotopically selective response for covert attention in the absence of significant visual stimulation using a threshold-contrast detection task. SC neurons have a laminar organization according to their function, with visually responsive neurons present in the superficial layers and visuomotor neurons in the intermediate layers. The results show that the response evoked by the threshold-contrast detection task is significantly deeper than the response evoked by the high-contrast speed discrimination task, reflecting a functional dissociation of the attentional enhancement of visuomotor and visual neurons, respectively. Such a functional dissociation of attention within SC laminae provides a subcortical basis for the oculomotor theory of attention.

Do head-on-trunk signals modulate disengagement of spatial attention?

Body schema is indispensable for sensorimotor control and learning, but whether it is associated with cognitive functions, such as allocation of spatial attention, remains unclear. Observations in patients with unilateral spatial neglect support this view, yet data from neurologically normal participants are inconsistent. Here, we investigated the influence of head-on-trunk positions (30° left or right, straight ahead) on disengagement of attention in healthy participants. Five experiments examined the effects of valid or invalid cues on spatial shifts of attention using the Posner paradigm. Experiment 1 used a forced-choice task. Participants quickly reported the location of a target that appeared left or right of the fixation point, preceded by a cue on the same (valid) or opposite side (invalid). Experiments 2, 3, and 4 also used valid and invalid cues but required participants to simply detect a target appearing on the left or right side. Experiment 5 used a speeded discrimination task, in which participants quickly reported the orientation of a Gabor. We observed expected influences of validity and stimulus onset asynchrony as well as inhibition of return; however, none of the experiments suggested that head-on-trunk position created or changed visual field advantages, contrary to earlier reports. Our results showed that the manipulations of the body schema did not modulate attentional processes in the healthy brain, unlike neuropsychological studies on neglect patients. Our findings suggest that spatial neglect reflects a state of the lesioned brain that is importantly different from that of the normally functioning brain.

Children Cautious Strategy and Variable Maturation Time Window for Responding in a Visual Search Task

Present study evaluates the changes and developmental trajectories of the attentional serial visual search and pre-attentional parallel search (pop-out) in situations in which a fast response is required. The hypothesis of present study are 1) that pre-attentional selection mechanisms develop before than serial attentional processes; 2) in the most difficult tasks, children prefer to adopt a non-responding strategy to an impulsive response patters; and 3) in speeded difficult discrimination tasks young children arrives to the criteria of correct performance in a broad temporal window. The results showed an inverse relationship between the age and the RTs and the different type of errors. For the present set of stimuli which produces an overcrowded scene and required a fast response, the behavioural trend of normal children is to the non-response pattern rather than to impulsive incorrect responses pattern. It can be suggested that young normal children present a broad temporal window to obtain the perceptual, motor and/or cognitive skills needed for responding adequately in a fast speeded discrimination task.

Spatial Attention Is Attracted in a Sustained Fashion toward Singular Points in the Optic Flow

While a single approaching object is known to attract spatial attention, it is unknown how attention is directed when the background looms towards the observer as s/he moves forward in a quasi-stationary environment. In Experiment 1, we used a cued speeded discrimination task to quantify where and how spatial attention is directed towards the target superimposed onto a cloud of moving dots. We found that when the motion was expansive, attention was attracted towards the singular point of the optic flow (the focus of expansion, FOE) in a sustained fashion. The effects were less pronounced when the motion was contractive. The more ecologically valid the motion features became (e.g., temporal expansion of each dot, spatial depth structure implied by distribution of the size of the dots), the stronger the attentional effects. Further, the attentional effects were sustained over 1000 ms. Experiment 2 quantified these attentional effects using a change detection paradigm by zooming into or out of photographs of natural scenes. Spatial attention was attracted in a sustained manner such that change detection was facilitated or delayed depending on the location of the FOE only when the motion was expansive. Our results suggest that focal attention is strongly attracted towards singular points that signal the direction of forward ego-motion.

Neural response to the second stimulus associated with poor speed discrimination performance in schizophrenia

Visual motion processing is compromised in schizophrenia (SZ), but it is uncertain what neural deviations account for their motion analysis abnormalities. Neural activations were measured with dense-array electroencephalography while 14 medicated SZ and 14 healthy persons performed a paired-stimuli forced choice speed discrimination task. SZ had (a) worse-at-speed discrimination, replicating previous findings, (b) normal early extrastriate neural activity (N1) to both motion stimuli, (c) reduced later extrastriate activity (P2) specifically to the second stimulus, and (d) following P2, an enhanced later N2 over parietal cortex. Stronger P2 and N2 responses were associated with better speed discrimination performance across groups. These findings indicate that the neural correlates of poor motion analysis in SZ may not be an early visual analysis abnormality but a problem with efficient use of speed information later in cognitive processing.

General and specific perceptual learning in radial speed discrimination

The specificity of learning in speed discrimination was examined in three psychophysical experiments. In Experiment 1, half of the observers trained with inward motion direction on a speed discrimination task, whereas the other half trained on the same task but with outward motion direction. The results indicated that significant training-based improvement transferred from a trained radial direction to an untrained radial direction. Experiment 2 confirmed this transfer by showing that complete transfer was obtained even when stimuli moving in an untrained radial direction were used in the transfer task. In Experiment 3, observers were trained at a viewing distance of 114 cm. The results showed that learning transferred partly to the viewing distances of 57 cm and 228 cm. In summary, the present transfer results indicate that reliable generalizations can be obtained in perceptual learning of radial speed discrimination.

Topography of Covert Visual Attention in Human Superior Colliculus

Experiments were performed to examine the topography of covert visual attention signals in human superior colliculus (SC), both across its surface and in its depth. We measured the retinotopic organization of SC to direct visual stimulation using a 90° wedge of moving dots that slowly rotated around fixation. Subjects (n = 5) were cued to perform a difficult speed-discrimination task in the rotating region. To measure the retinotopy of covert attention, we used a full-field array of similarly moving dots. Subjects were cued to perform the same speed-discrimination task within a 90° wedge-shaped region, and only the cue rotated around fixation. High-resolution functional magnetic resonance imaging (fMRI, 1.2 mm voxels) data were acquired throughout SC. These data were then aligned to a high-resolution T1-weighted reference volume. The SC was segmented in this volume so that the surface of the SC could be computationally modeled and to permit calculation of a depth map for laminar analysis. Retinotopic maps were obtained for both direct visual stimulation and covert attention. These maps showed a similar spatial distribution to visual stimulation maps observed in rhesus macaque and were in registration with each other. Within the depth of SC, both visual attention and stimulation produced activity primarily in the superficial and intermediate layers, but stimulation activity extended significantly more deeply than attention.

Humans do not have direct access to retinal flow during walking

Perceived visual speed has been reported to be reduced during walking. This reduction has been attributed to a partial subtraction of walking speed from visual speed (F. H. Durgin & K. Gigone, 2007; F. H. Durgin, K. Gigone, & R. Scott, 2005). We tested whether observers still have access to the retinal flow before subtraction takes place. Observers performed a 2IFC visual speed discrimination task while walking on a treadmill. In one condition, walking speed was identical in the two intervals, while in a second condition walking speed differed between intervals. If observers have access to the retinal flow before subtraction, any changes in walking speed across intervals should not affect their ability to discriminate retinal flow speed. Contrary to this "direct access hypothesis," we found that observers were worse at discrimination when walking speed differed between intervals. The results therefore suggest that observers do not have access to retinal flow before subtraction. We also found that the amount of subtraction depended on the visual speed presented, suggesting that the interaction between the processing of visual input and of self-motion is more complex than previously proposed.

Learning of timing patterns and the development of temporal expectations

The present study investigated the learning of a culturally unfamiliar musical rhythm, leading to the development of temporal expectations, and it explored the potential for generalization across tempi and tasks. With that aim, we adapted the serial reaction time task to examine the learning of temporal structures by an indirect method. The temporal pattern employed was based on a complex interval ratio (2:3) and compared to one based on a simple interval ratio (1:2). In the exposure phase, non-musician participants performed a two-choice speeded discrimination task that required responding by key press to each event of the simple or complex auditory pattern. Participants were not informed about the temporal regularities; their task solely concerned the discrimination task. During exposure (Experiments 1-3), response times decreased over time for both temporal patterns, but particularly for the events following the longer interval of the more complex 2:3 pattern. Exposure further influenced performance in subsequent testing phases, notably the precision of tap timing in a production task (Experiment 2) and temporal expectations in a perception task (Experiment 3). Our findings promote the new paradigm introduced here as a method to investigate the learning of temporal structures.

Perceptual learning and adaptation in the perception of self motion

When perceptual systems adapt they may be sacrificing accuracy for precision. By allocating the existing coding apparatus so as to tune its range to the locally experienced stimulus space, adaptation processes can enhance the discriminability of likely stimuli. For example, the tight coupling of perception and action during locomotion provides an important informational substrate for improving perceptual discrimination. We have found that the perceptual discrimination of optic flow speed is automatically tuned to walking speed such that perceived flow rates are reduced during walking. However, contrary to threshold elevation accounts of this phenomenon, perceptual discrimination is actually reliably enhanced for flow speeds appropriate to walking. To measure this we used a 2IFC speed discrimination task administered in a wide-area virtual reality apparatus that allowed us full control over the visual speeds presented during natural walking. In two experiments it was found that discrimination performance deteriorated dramatically for visual speeds less than 40% of walking speed, but showed striking and consistent improvement for visual speeds near to and above walking speed. It is as if the entire coding space available for visual motion is dynamically reallocated when walking — leaving slow visual motions undetectable, but enhancing the discrimination of self-motion-relevant visual speeds. Although many vivid demonstrations of perceptual aftereffects seem to show that perceptual systems are susceptible to error and bias, techniques that look for the gains in perceptual precision and sensitivity may be more revealing.

Representation of stimulus speed in prefrontal cortex during speed discrimination task

Representation of stimulus speed in prefrontal cortex during speed discrimination task

On the perceptual basis of distinctive features: Evidence from the perception of fricatives by Dutch and English speakers

Two speech perception experiments explored the auditory basis of distinctive features. Experiment 1 found that Dutch listeners rated [s] and [ʃ] as more similar to each other than American English listeners did. We attributed this to the lack of a phonemic distinction between [s] and [ʃ] in Dutch phonology in addition to their relationship via a productive phonological rule in Dutch. Experiment 1 also found that Dutch listeners rated [θ] and [s], and [θ] and [ʃ] as more similar to each other than did American English listeners. We attributed this to the lack of [θ] in the Dutch inventory. Experiment 2 found that Dutch and American English listeners did not significantly differ from each other in a speeded discrimination task with the same stimuli as Experiment 1. Reaction times in Experiment 2 were highly correlated with the rating data of Experiment 1 indicating that the general pattern of response in Experiment 1 was based on auditory similarity, with language-specific effects superimposed on the general pattern. The auditory basis of distinctive features found here accords with Stevens’ (1989) quantal theory account of the feature [±anterior]. We conclude that phonetic similarity is comprised of three components: (1) auditory similarity, (2) phonetic inventory, and (3) language-specific patterns of alternation.

Electrophysiological correlates of learning-induced modulation of visual motion processing in humans

Training on a visual task leads to increased perceptual and neural responses to visual features that were attended during training as well as decreased responses to neglected distractor features. However, the time course of these attention-based modulations of neural sensitivity for visual features has not been investigated before. Here we measured event related potentials (ERP) in response to motion stimuli with different coherence levels before and after training on a speed discrimination task requiring object-based attentional selection of one of the two competing motion stimuli. We found that two peaks on the ERP waveform were modulated by the strength of the coherent motion signal; the response amplitude associated with motion directions that were neglected during training was smaller than the response amplitude associated with motion directions that were attended during training. The first peak of motion coherence-dependent modulation of the ERP responses was at 300 ms after stimulus onset and it was most pronounced over the occipitotemporal cortex. The second peak was around 500 ms and was focused over the parietal cortex. A control experiment suggests that the earlier motion coherence-related response modulation reflects the extraction of the coherent motion signal whereas the later peak might index accumulation and readout of motion signals by parietal decision mechanisms. These findings suggest that attention-based learning affects neural responses both at the sensory and decision processing stages.

Stimulant Treatment Reduces Lapses in Attention among Children with ADHD: The Effects of Methylphenidate on Intra-Individual Response Time Distributions

Recent research has suggested that intra-individual variability in reaction time (RT) distributions of children with ADHD is characterized by a particularly large rightward skew that may reflect lapses in attention. The purpose of the study was to provide the first randomized, placebo-controlled test of the effects of the stimulant methylphenidate (MPH) on this tail and other RT distribution characteristics. Participants were 49 9- to 12-year-old children with ADHD. Children participated in a 3-day double-blind, placebo-controlled medication assessment during which they received long-acting MPH (Concerta), with the nearest equivalents of 0.3 and 0.6 mg/kg t.i.d. immediate-release MPH. Children completed a simple two-choice speeded discrimination task on and off of medication. Mode RT and deviation from the mode were used to examine the peak and skew, respectively, of RT distributions. MPH significantly reduced the peak and skew of RT distributions. Importantly, the two medication effects were uncorrelated suggesting that MPH works to improve both the speed and variability in responding. The improvement in variability with stimulant treatment is interpreted as a reduction in lapses in attention. This, in turn, may reflect stimulant enhancement of self-regulatory processes theorized to be at the core of ADHD.

Do we have direct access to retinal image motion during smooth pursuit eye movements?

One way the visual system estimates object motion during pursuit is to combine estimates of eye velocity and retinal motion. This questions whether observers need direct access to retinal motion during pursuit. We tested this idea by varying the correlation between retinal motion and objective motion in a two-interval speed discrimination task. Responses were classified according to three motion cues: retinal speed (based on measured eye movements), objective speed, and the relative motion between pursuit target and stimulus. In the first experiment, feedback was based on relative motion and this cue fit the response curves best. In the second experiment, simultaneous relative motion was removed but observers still used the sequential relative motion between pursuit target and dot pattern to make their judgements. In a final experiment, feedback was given explicitly on the retinal motion, using online measurements of eye movements. Nevertheless, sequential relative motion still provided the best account of the data. The results suggest that observers do not have direct access to retinal motion when making perceptual judgements about movement during pursuit.

Sensory dominance in combinations of audio, visual and haptic stimuli

Participants presented with auditory, visual, or bi-sensory audio-visual stimuli in a speeded discrimination task, fail to respond to the auditory component of the bi-sensory trials significantly more often than they fail to respond to the visual component--a 'visual dominance' effect. The current study investigated further the sensory dominance phenomenon in all combinations of auditory, visual and haptic stimuli. We found a similar visual dominance effect also in bi-sensory trials of combined haptic-visual stimuli, but no bias towards either sensory modality in bi-sensory trials of haptic-auditory stimuli. When presented with tri-sensory trials of combined auditory-visual-haptic stimuli, participants made more errors of responding only to two corresponding sensory signals than errors of responding only to a single sensory modality, however, there were no biases towards either sensory modality (or sensory pairs) in the distribution of both types of errors (i.e. responding only to a single stimulus or to pairs of stimuli). These results suggest that while vision can dominate both the auditory and the haptic sensory modalities, it is limited to bi-sensory combinations in which the visual signal is combined with another single stimulus. However, in a tri-sensory combination when a visual signal is presented simultaneously with both the auditory and the haptic signals, the probability of missing two signals is much smaller than of missing only one signal and therefore the visual dominance disappears.

Differential activation patterns of occipital and prefrontal cortices during motion processing: Evidence from normal and schizophrenic brains

Visual motion perception is normally mediated by neural processing in the posterior cortex. Focal damage to the middle temporal area (MT), a posterior extrastriate region, induces motion perception impairment. It is unclear, however, how more broadly distributed cortical dysfunction affects this visual behavior and its neural substrates. Schizophrenia manifests itself in a variety of behavioral and perceptual abnormalities that have proved difficult to understand through a dysfunction of any single brain system. One of these perceptual abnormalities involves impaired motion perception. Motion processing provides an opportunity to clarify the roles of multiple cortical networks in both healthy and schizophrenic brains. Using fMRI, we measured cortical activation while participants performed two visual motion tasks (direction discrimination and speed discrimination) and one nonmotion task (contrast discrimination). Normal controls showed robust cortical activation (BOLD signal changes) in MT during the direction and speed discrimination tasks, documenting primary processing of sensory input in this posterior region. In patients with schizophrenia, cortical activation was significantly reduced in MT and significantly increased in the inferior convexity of the prefrontal cortex, an area that is normally involved in higher level cognitive processing. This shift in cortical responses from posterior to prefrontal regions suggests that motion perception in schizophrenia is associated with both deficient sensory processing and compensatory cognitive processing. Furthermore, this result provides evidence that in the context of broadly distributed cortical dysfunction, the usual functional specificity of the cortex becomes modified, even across the domains of sensory and cognitive processing.