Further evidence that object-based correspondence effects are primarily modulated by object location not by grasping affordance

Tipper, Paul and Hayes found object-based correspondence effects for door-handle stimuli for shape judgments but not colour. They reasoned that a grasping affordance is activated when judging dimensions related to a grasping action (shape), but not for other dimensions (colour). Cho and Proctor, however, found the effect with respect to handle position when the bases of the door handles were centred (so handles were positioned left or right; the base-centred condition) but not when the handles were centred (the object-centred condition), suggesting that the effect is driven by object location, not grasping affordance. We conducted an independent replication of Cho and Proctor's design, but with behavioural and event-related potential measures. Participants made shape judgments in Experiment 1 and colour judgments in Experiment 2 on the same door-handle objects. Correspondence effects on response time and errors were obtained in both experiments for the base-centred condition but not the object-centred condition. Effects were absent in the P1 and N1 data, which are consistent with the hypothesis of little binding between visual processing of grasping component and action. These findings question the grasping-affordance view but support a spatial-coding view, suggesting that correspondence effects are modulated primarily by object location.     

Do kinematic metrics of walking balance adapt to perturbed optical flow?

Visual (i.e., optical flow) perturbations can be used to study balance control and balance deficits. However, it remains unclear whether walking balance control adapts to such perturbations over time. Our purpose was to investigate the propensity for visuomotor adaptation in walking balance control using prolonged exposure to optical flow perturbations. Ten subjects (age: 25.4 ± 3.8 years) walked on a treadmill while watching a speed-matched virtual hallway with and without continuous mediolateral optical flow perturbations of three different amplitudes. Each of three perturbation trials consisted of 8 min of prolonged exposure followed by 1 min of unperturbed walking. Using 3D motion capture, we analyzed changes in foot placement kinematics and mediolateral sacrum motion. At their onset, perturbations elicited wider and shorter steps, alluding to a more cautious, general anticipatory balance control strategy. As perturbations continued, foot placement tended toward values seen during unperturbed walking while step width variability and mediolateral sacrum motion concurrently increased. Our findings suggest that subjects progressively shifted from a general anticipatory balance control strategy to a reactive, task-specific strategy using step-to-step adjustments. Prolonged exposure to optical flow perturbations may have clinical utility to reinforce reactive, task-specific balance control through training.     

Vernier acuity and the magnocellular system revisited: Response to Skottun and Skoyles

Skottun and Skoyles (2009) recently presented a comment on Vernier acuity and magnocellular dysfunctions in fragile X premutation carriers (Kéri & Benedek, 2009). The authors concluded that our finding that the magnocellular deficit, as revealed by luminance-contrast sensitivity measurements, is associated with impaired Vernier acuity for achromatic gratings does not mean that this procedure is suitable for the investigation of the magnocellular pathways, given that deficits outside the magnocellular system also lead to impaired Vernier acuity. However, Skottun and Skoyles (2009) did not consider the dissociation between achromatic and isoluminant color Vernier and the convergence of Vernier and luminance-contrast sensitivity measurements.     

Subjective discriminability of invisibility: A framework for distinguishing perceptual and attentional failures of awareness

Conscious visual perception can fail in many circumstances. However, little is known about the causes and processes leading to failures of visual awareness. In this study, we introduce a new signal detection measure termed subjective discriminability of invisibility (SDI) that allows one to distinguish between subjective blindness due to reduction of sensory signals or to lack of attentional access to sensory signals. The SDI is computed based upon subjective confidence in reporting the absence of a target (i.e., miss and correct rejection trials). Using this new measure, we found that target misses were subjectively indistinguishable from physical absence when contrast reduction, backward masking and flash suppression were used, whereas confidence was appropriately modulated when dual task, attentional blink and spatial uncertainty methods were employed. These results show that failure of visual perception can be identified as either a result of perceptual or attentional blindness depending on the circumstances under which visual awareness was impaired.     

On the relations between action planning, object identification, and motor representations of observed actions and objects

Recent evidence suggests that viewing a static prime object (a hand grasp), can activate action representations that affect the subsequent identification of graspable target objects. The present study explored whether stronger effects on target object identification would occur when the prime object (a hand grasp) was made more action-rich and dynamic. Of additional interest was whether this type of action prime would affect the generation of motor activity normally elicited by the target object. Three experiments demonstrated that grasp observation improved the identification of grasp-congruent target objects relative to grasp-incongruent target objects. We argue from this data that identifying a graspable object includes the processing of its action-related attributes. In addition, grasp observation was shown to influence the motor activity elicited by the target object, demonstrating interplay between action-based and object-based motor coding.     

Perceiving the present and a systematization of illusions

Over the history of the study of visual perception there has been great success at discovering countless visual illusions. There has been less success in organizing the overwhelming variety of illusions into empirical generalizations (much less explaining them all via a unifying theory). Here, this article shows that it is possible to systematically organize more than 50 kinds of illusion into a 7 × 4 matrix of 28 classes. In particular, this article demonstrates that (1) smaller sizes, (2) slower speeds, (3) greater luminance contrast, (4) farther distance, (5) lower eccentricity, (6) greater proximity to the vanishing point, and (7) greater proximity to the focus of expansion all tend to have similar perceptual effects, namely, to (A) increase perceived size, (B) increase perceived speed, (C) decrease perceived luminance contrast, and (D) decrease perceived distance. The detection of these empirical regularities was motivated by a hypothesis, called "perceiving the present," that the visual system possesses mechanisms for compensating neural delay during forward motion. This article shows how this hypothesis predicts the empirical regularity.     

Attention attenuates metacontrast masking

The influence of attention on perceptual awareness was examined using metacontrast masking. Attention was manipulated with endogenous cues to assess the effects on the temporal and spatial parameters of target visibility. Experiment 1 examined the time course of effective masking when the target and mask set were presented at an attended vs. an unattended location. The valid allocation of attention decreased the magnitude of the masking effect (i.e. increased visibility) for approximately 80 ms. Furthermore, even with spatial displacements of the target and mask and center-to-center separations of 1.5 degrees or 2.7 degrees of visual angle (Experiment 2), target visibility was increased when attention was validly allocated. These results indicate that attention influences low-level visual processes to enhance visual awareness.     

Visual pathway deficit in female fragile X premutation carriers: a potential endophenotype

Previous studies indicated impaired magnocellular (M) and relatively spared parvocellular (P) visual pathway functioning in patients with fragile X syndrome. In this study, we assessed M and P pathways in 22 female fragile X premutation carriers with normal intelligence and in 20 healthy non-carrier controls. Testing procedure included visual contrast sensitivity and vernier threshold measurements. Results revealed that carriers were selectively impaired on tests of M pathways (low spatial/high temporal frequency contrast sensitivity and frequency-doubling vernier), whereas they showed intact performance on P pathway tests. These results suggest that the deficit of the M pathway is an endophenotype of fragile X syndrome.     

Perception of exertion and attention allocation as a function of visual and auditory conditions

AimThe aim of the present study was to test the role of auditory (e.g., music) and visual sensory modalities on perceived levels of exertion and attention processes across a 30% dynamometer-squeezing task. The study explored the dynamics embedded within the automated nature of the association–dissociation shift process.MethodSixty young adults (33 male and 27 female; M_age = 22.21 yrs, SD = 3.49) were recruited to perform a handgrip-squeezing task. They were randomly assigned to 4 groups of 15 participants. After establishing the maximal squeezing value they performed 30% max squeezing-task under one of four assigned condition: full vision and preferred music, full vision and no music, blindfolded and preferred music, and blindfolded and no music until volitional fatigue. Rate of perceived exertion and attention strategies were administered at 30 s intervals.ResultsA set of Repeated Measures ANOVAs indicated an additive effect of visual and auditory cues on the perception of exertion, and the dynamic pattern of attention shift. Participants who were given both forms of sensory information remained in a dissociative strategy for a significantly longer duration than participants in all other conditions.ConclusionsSeveral sensory modalities are required to affect perceived exertion and attention allocation while engaging in demanding workload. External stimuli may serve as mediating agents in diverting attention away from internal and painful stimuli. This distraction may likely contribute to the pleasantness of the exercise experience, ultimately leading to increased exercise participation and reduced dropout rates.     

Foveal-to-peripheral priming in letter identification reflects response bias, not enhanced visibility

Several studies have suggested that it might be easier to identify a letter when its replication is simultaneously presented in the visual display. We have measured identification accuracy for a memorized target letter that was shown in the peripheral field in two conditions in which a letter either identical or different in shape was flashed simultaneously at fixation. The results of three forced-choice experiments showed that, contrary to Geiger and Lettvin's (1986) previous findings, an identity prime did not improve the visibility of a temporally backward masked target letter. However, the foveal prime letter could apparently bias the subject's decision so that he/she was much more ready to report the more visible prime letter as the peripheral target.