Blindsight is unlike normal conscious vision: evidence from an exclusion task

We explored whether information processed subconsciously in blindsight is qualitatively different from normal conscious processing. On each trial the blindsight patient GY was presented with a square-wave grating either in an upper or lower quadrant of his visual field and was asked to report the opposite of its location (e.g. to say 'Up' if it was in the lower quadrant). We found that while GY was able to follow these exclusion instructions in his normal field, he tended to erroneously respond with the real location when the grating appeared in his blind field. Remarkably, his error rate actually increased with increasing grating contrast in his blind field. The interpretation of these results does not rely on subjective reports and thus cannot be criticized on the grounds that subjective reports are unreliable. We conclude that blindsight is unlike normal conscious vision.     

External focus of attention improves performance in a speeded aiming task

Athletic skills are often executed better when learners focus attention externally (e.g., on the trajectory of the ball after a tennis serve), rather than internally (e.g., on the position of their arm) (e.g., Wulf, 2007a). The current study explored the effects of attention focus on learning of speeded responses, and examined whether these benefits hold for retention and transfer. Participants performed a computerized speeded aiming task while focusing on the direction of the cursor (external focus) versus the direction in which their hand moved the mouse (internal focus). One week later, half of the participants performed the same task again (retention), and half performed the task under conditions in which the mouse movements were changed (transfer). Relative to internal focus, external focus led to faster acquisition and better maintenance of speeded responses over the retention interval.     

The effects of age and task context on Stroop task performance

In this study, we investigated the impact of age and task context on Stroop task performance, using error scores, response latencies, and process dissociation estimates (e.g., Lindsay & Jacoby, 1994). Across three experiments, the findings showed that although older adults were able to evaluate Stroop task demands and modify their representations of task context in response to this knowledge, they were less able to maintain and update these representations on a trial-by-trial basis in tasks with high stimulus uncertainty or ambiguity. Moreover, although there was no age-related decline in the ability to modulate print color information, older adults were consistently less able to control the activation of conflicting word information. Together, these findings suggest that whereas age differences in the Stroop task may be magnified under conditions that promote transient failures to maintain task context, the primary source of these differences seems to be a more enduring decline in the efficiency of processes that are responsible for suppressing the activation of irrelevant lexical information.     

Private speech on an executive task: relations with task difficulty and task performance

Measures of private speech and task performance were obtained for a sample of 46 5- and 6-year-olds engaged on a mechanical version of the Tower of London (ToL) task. Two different sets of four puzzles of increasing difficulty were attempted on two occasions. In line with Vygotskian predictions, there was a quadratic relation between private speech and task difficulty, but no evidence of a shift towards self-regulatory sub-types of private speech with increasing task difficulty. Levels of self-regulatory private speech were significantly related to concurrent, but not subsequent, task performance. We discuss the significance of these findings for the Vygotskian view that private speech has an adaptive function in the self-regulation of behaviour.     

Changes in spinal excitability during dual task performance

ABSTRACT The authors investigated how the nervous system responds to dual task performance. Because dual tasking is associated with greater postural challenges, it was hypothesized that spinal excitability would be reduced when simultaneously performing 2 tasks. For this experiment, participants maintained a lying or standing posture with or without performing a concurrent cognitive task (i.e., reacting to an auditory tone). Spinal excitability was assessed by eliciting the soleus Hoffmann reflex (H-reflex). Results indicated that the H-reflex was 6.4 ± 2.3% smaller (p = .011) when dual compared to single tasking. The reduced H-reflex amplitude, indicating a depressed spinal excitability, when dual tasking is suggested to reflect a neural strategy that individuals adopt to maintain postural stability when cognitive resources are divided between 2 concurrent tasks.     

Practice and assimilation effects in a multilimb aiming task

When two limbs are required to move different distances simultaneously, assimilation effects are shown: The shorter distance limb tends to overshoot the target, whereas the longer distance limb undershoots. The effect of practice on assimilation effects was studied in two experiments, using a simultaneous four-limb aiming task. When subjects were required to move their left limbs a shorter distance than the right (5 cm vs. 9 cm), the right limbs moved a lesser distance and had greater variable and overall errors relative to a group required to move all limbs the same distance (9 cm). Practice reduced assimilation effects in the lower limbs, but spatial assimilations were present throughout 125 acquisition trials with KR and 50 no-KR transfer trials, spanning 24 hours. When the upper limbs were required to move a greater distance than the lower limbs (15 cm vs. 9 cm), the lower limbs showed longer distances and increased overall errors early in practice compared to the lower limbs of a group required to move all limbs 9 cm. With practice, the between-group differences decreased, with no assimilation effects shown on the transfer trials. The results suggest that neural crosstalk is greater between left and right sides than between upper and lower limbs. Results are discussed in light of the functional cerebral space model of simultaneous actions.     

Effects of anxiety,a cognitive secondary task,and expertise on gaze behavior and performance in a far aiming task

ObjectivePrevious studies focused on investigating the separate effects of anxiety, cognitive load, and expertise on perceptual-motor performance, but the combined effects of these factors have not been studied yet. The objective of the current study was to investigate these factors in combination.DesignEleven expert dart players and nine novices performed a dart throwing task in low-anxiety (LA) and high-anxiety (HA) conditions with and without a secondary task.MethodTo manipulate anxiety the dart throwing task was performed low (LA) and high (HA) on a climbing wall with and without the secondary counting backwards task. Performance and efficiency of task execution and gaze behavior were assessed.ResultsThe anxiety manipulation evoked a decrease in dart performance, but only for the novices. Increases in mental effort and dart times and a decrease in response rate on the secondary task were observed for both groups. This shows that there were decreases in processing efficiency with anxiety. Most important, the anxiety-induced decrease in performance for the novices was accompanied by final fixations on the target that were substantially shorter and deviated off the target earlier. The dual task did not affect performance.ConclusionAnxiety affects efficiency and sometimes performance in far aiming tasks. Changes are accompanied by changes in gaze behavior, particularly the final fixation on the target. All in all, findings provide support for Attentional Control Theory as a suitable framework to explain the effects of anxiety, a cognitive secondary task, and expertise in far aiming tasks.     

Lost ability to automatize task performance in old age

Can elderly adults automatize a new task? To address this question, 10 older adults each performed 10,080 training trials over 12 sessions on an easy but novel task. The psychological refractory period (PRP) procedure was then used to evaluate whether this highly practiced task, when presented as task 2 along with an unpracticed task 1, could proceed automatically. If automatic, task 2 processing should bypass the bottleneck and, therefore, not be delayed while central attention is devoted to task 1, yielding little dual-task interference. This is exactly what Maquestiaux, Laguë-Beauvais, Ruthruff, and Bherer (Memory and Cognition 36:1262-1282, 2008) previously observed for almost all younger adults, even with half the training on a more difficult task. Although extensive training reduced older adults’ reaction times to only 307 ms, a value virtually identical to that attained by Maquestiaux et al.’s (Memory and Cognition 36:1262-1282, 2008) younger adults, the highly practiced task 2 was slowed by 485 ms in the dual-task PRP procedure. Such a large slowing in older adults is striking given the easy tasks and massive amounts of practice. These findings demonstrate a qualitative change with age, in which older adults lose the ability to automatize novel tasks, which cannot be attributed merely to generalized cognitive slowing.     

The effects of age and task domain on dual task performance: A meta-analysis

Recent research has provided mixed findings as to whether older adults find dual tasking problematic. Here, we examined whether methodological variations across studies can account for the discrepancies in the literature. Meta-analyses conducted on the results of 34 studies conducted between 1981 and 2003 found a strong overall effect size (d = .68), which indicated a clear age-related dual tasking impairment. However, this effect size was not representative of all the individual studies reported. Subsequent analyses, using an analysis of variance analogue (Hedges & Olkin, 1985), investigated potential moderators responsible for the variability in the effect sizes across studies. These secondary analyses included a comparison of dependent measure used, whether baseline differences in performance had been controlled for, and task domain. Task domain was found to be the critical moderator variable. Notably, tasks with a substantial controlled processing, or motor component showed greater dual task impairment than tasks that were relatively simple or relied on automatic processing.     

The dual role of vision in sequential aiming movements

Previous research has demonstrated that movement times to the first target in sequential aiming movements are influenced by the properties of subsequent segments. Based on this finding, it has been proposed that individual segments are not controlled independently. The purpose of the current study was to investigate the role of visual feedback in the interaction between movement segments. In contrast to past research in which participants were instructed to minimize movement time, participants were set a criterion movement time and the resulting errors and limb trajectory kinematics were examined under vision and no vision conditions. Similar to single target movements, the results indicated that vision was used within each movement segment to correct errors in the limb trajectory. In mediating the transition between segments, visual feedback from the first movement segment was used to adjust the parameters of the second segment. Hence, increases in variability that occurred from the first to the second target in the no vision condition were curtailed when visual feedback was available. These results are discussed along the lines of the movement constraint and movement integration hypotheses.     

Development of unimanual versus bimanual task performance in an isometric task

Sixty-three children between 5 and 12 years of age and 15 adults performed a unimanual and a bimanual isometric force task. The performance of the preferred hand in the unimanual task was compared to the performance of the preferred hand in the bimanual task. It was hypothesized that in the bimanual task the absolute error will be higher, there will be more irregularity and the participants will need more time due to the additional effort from the central nervous system, especially with respect to the communication between the hemispheres. Furthermore, in younger children bimanual force variability was expected to be higher due to developmental aspects concerning callosal maturation and attention. It was found that with respect to force generation the preferred hand was not affected by bilateral isometric force generation, but with respect to force regulation it was. The coefficient of variation (CV) of the force was 34% larger in the bimanual task as compared to the unimanual task. For the time to target force, the increase was 28%. With repetition of the trials the CV decreased in the bimanual task, but only in the youngest age group. During development there was no change in absolute error, yet there was a major reduction in force variability in the bimanual task. It is suggested that improvement in interhemispheric communication and in the ability to focus attention plays a role in the decrease in variability with age.     

Dual-task performance as a function of adult age and task complexity

A dual-task procedure was used to examine capacity demands of letter-matching in younger and older adults. Older subjects generally were slower on both tasks than were younger adults, but this difference was especially pronounced for the late stages of category matching, suggesting that retrieval and comparison of category information is particularly demanding for older adults.     

Rightward superiority of eye movements in a bimanual aiming task

To examine the role of visual monitoring in the between-hand differences in skilled manual movements, eye movements and performance during bimanual aiming tasks were analysed. When subjects were required to make bimanual aiming responses to symmetrically placed targets, they preferentially monitored the movements of the right hand, resulting in better performance on the right hand. In addition, manipulation of the subject's gaze showed that the movements of the right hand were more influenced by visual monitoring than those of the left hand. The results were interpreted as showing that the between-hand differences in skilled movements are mainly due to the different efficiency in the use of visual monitoring.     

A study of Fitts' law on goal-directed aiming task with moving targets

Most research based on Fitts' law define a log-linear relationship between temporal and spatial accuracy in goal-directed aiming tasks using stationary targets. Whether this relationship holds or not when the targets have varying velocities, and how the behavioral strategies and physical activities may change accordingly are of interest. The aim of this study was to investigate the relationship between temporal and spatial accuracy in goal-directed aiming tasks with moving targets. Participants were asked to aim at two target widths using a joystick. Results demonstrated that in a goal-directed aiming task there was a negative effect on performance when target velocity was increased or target width was decreased. Participants moved faster and then made more systematic errors in a high-velocity target condition. Results may be applicable to the complex perceptual-motor behavior of people who perform tasks using computers.     

How age affects memory task performance in clinically normal hearing persons

The main objective of this study is to investigate memory task performance in different age groups, irrespective of hearing status. Data are collected on a short-term memory task (WAIS-III Digit Span forward) and two working memory tasks (WAIS-III Digit Span backward and the Reading Span Test). The tasks are administered to young (20–30 years, n = 56), middle-aged (50–60 years, n = 47), and older participants (70–80 years, n = 16) with normal hearing thresholds. All participants have passed a cognitive screening task (Montreal Cognitive Assessment (MoCA)). Young participants perform significantly better than middle-aged participants, while middle-aged and older participants perform similarly on the three memory tasks. Our data show that older clinically normal hearing persons perform equally well on the memory tasks as middle-aged persons. However, even under optimal conditions of preserved sensory processing, changes in memory performance occur. Based on our data, these changes set in before middle age.     

The effects of music and task difficulty on performance at a visual vigilance task

Forty subjects performed a visual vigilance task in music or noise and when the task was difficult or easy. Response measures taken were: correct detections, commission errors, detection latencies and d' values. For the difficult version of the task a significant increase in detection latencies was found which music prevented. Broadly similar findings were obtained for correct detections. The results are compared with other studies of detection latency and task difficulty and are discussed in terms of arousal.     

Examining age differences in performance of a complex information search and retrieval task.

This study examined age differences in performance of a complex information search and retrieval task by using a simulated real-world task typical of those performed by customer service representatives. The study also investigated the influence of task experience and the relationships between cognitive abilities and task performance. One hundred seventeen participants from 3 age groups, younger (20-39 years). middle-aged (40-59 years), and older (60-75 years), performed the task for 3 days. Significant age differences were found for all measures of task performance with the exception of navigational efficiency and number of problems correctly navigated per attempt. There were also effects of task experience. The findings also indicated significant direct and indirect relations between component cognitive abilities and task performance.     

Colour vision is aligned with natural scene statistics at 4 months of age

Visual perception in adult humans is thought to be tuned to represent the statistical regularities of natural scenes. For example, in adults, visual sensitivity to different hues shows an asymmetry which coincides with the statistical regularities of colour in the natural world. Infants are sensitive to statistical regularities in social and linguistic stimuli, but whether or not infants’ visual systems are tuned to natural scene statistics is currently unclear. We measured colour discrimination in infants to investigate whether or not the visual system can represent chromatic scene statistics in very early life. Our results reveal the earliest association between vision and natural scene statistics that has yet been found: even as young as 4 months of age, colour vision is aligned with the distributions of colours in natural scenes.

Research Highlights

1. We find infants’ colour sensitivity is aligned with the distribution of colours in the natural world, as it is in adults.
2. At just 4 months, infants’ visual systems are tailored to extract and represent the statistical regularities of the natural world.
3. This points to a drive for the human brain to represent statistical regularities even at a young age.