The effect of Kanizsa’s compression illusion on reflexive saccades

When a horizontal line is occluded by a surface, subjects misperceive the line as being compressed, that is, they perceive it to be shorter than it really is (Kanizsa’s compression illusion). The size of the compression effect usually ranges from approximately 5 to 10%. In this experiment, subjects executed reflexive saccades from one end of a line, presented at fixation, to the other end, with and without an occluding square. Saccade amplitude was reduced in all subjects in the presence of an occluding square; the effect averaged about 5%. These results demonstrate that saccade amplitude is modified by the Kanizsa compression illusion. They provide further evidence that reflexive saccade amplitude can be altered by illusion inducing stimuli, to the same degree as perceptual effects, even in circumstances in which other motor behaviours resist the illusion. They are difficult to reconcile with any strong version of the “two visual systems hypothesis”.     

The type of visual information mediates eye and hand movement bias when aiming to a Müller–Lyer illusion

Aiming bias typically influences perception but action towards the illusory stimulus is often unaffected. Recent studies, however, have shown that the type of information available is a predictor for the expression of action bias. In the present cyclical aiming experiment, the type of information (retinal and extra-retinal) was manipulated in order to investigate the differential contributions of different cues on both eye and hand movements. The results showed that a Müller-Lyer illusion caused very similar perturbation effects on hand and eye-movement amplitudes and this bias was mediated by the type of information available on-line. Interestingly, the impact of the illusion on goal-directed movement was smaller, when information about the figure but not the hand was provided for on-line control. Saccadic information did not influence the size of the effect of a Müller-Lyer illusion on hand movements. Furthermore, the illusions did not alter the eye-hand coordination pattern. The timing of saccade termination was strongly linked to hand movement kinematics. The present results are not consistent with current dichotomous models of perception and action or movement planning and on-line control. Rather, they suggest that the type of information available for movement planning mediates the size of the illusory effects. Overall, it has been demonstrated that movement planning and control processes are versatile operations, which have the ability to adapt to the type of information available.     

The effect of the Müller-Lyer illusion on saccades is modulated by spatial predictability and saccadic latency

Studies investigating the effect of visual illusions on saccadic eye movements have provided a wide variety of results. In this study, we test three factors that might explain this variability: the spatial predictability of the stimulus, the duration of the stimulus and the latency of the saccades. Participants made a saccade from one end of a Müller-Lyer figure to the other end. By changing the spatial predictability of the stimulus, we find that the illusion has a clear effect on saccades (16%) when the stimulus is at a highly predictable location. Even stronger effects of the illusion are found when the stimulus location becomes more unpredictable (19–23%). Conversely, manipulating the duration of the stimulus fails to reveal a clear difference in illusion effect. Finally, by computing the illusion effect for different saccadic latencies, we find a maximum illusion effect (about 30%) for very short latencies, which decreases by 7% with every 100 ms latency increase. We conclude that spatial predictability of the stimulus and saccadic latency influences the effect of the Müller-Lyer illusion on saccades.     

When does action resist visual illusions? Effector position modulates illusory influences on motor responses

Actors viewed horizontal segments either in isolation or embedded in patterns that produce spatial illusory effects (Kanizsa's compression illusion and the "dumbbell" version of the Müller-Lyer compression-expansion illusion). They were asked to reproduce the apparent horizontal extent of these segments by the amplitude of open- or closed-loop motor responses (after having positioned a finger on position A, choose a position B on the right of A such that apparent width = B–A). A touchmonitor was used to present the displays and to record movement amplitudes and times. In open-loop motor responses, displays were turned off as soon as actors raised their finger from position A. In closed-loop responses, displays could be viewed continuously during the actions. Four conditions were investigated: (1) open-loop responses starting from A at the right endpoint of the segment; (2) closed-loop responses from A at the right endpoint of the segment; (3) open-loop responses from A at the left endpoint of the segment; and (4) open-loop responses from A aligned horizontally with the left endpoint of the segment but displaced vertically below that segment. With both kinds of display, results in conditions (1) and (2) demonstrated illusory effects comparable to those measured in standard visual matching experiments, whereas results in conditions (3) and (4) showed essentially no illusory effects. Implications for models of visuomotor transformations in peripersonal space are discussed.     

Grasping the Müller–Lyer illusion: not a change in perceived length

Peak grip aperture has often been used to quantify the influence of illusions on judgments of size for action. However, a larger peak grip aperture need not mean that the object looks larger. It could also mean that it was grasped more carefully. These two possibilities can be distinguished on the basis of the velocity of grip closure just before contact. We let people grasp a bar that was placed on the shaft of a Müller–Lyer figure. The Müller–Lyer figure influenced the peak grip aperture. It did not influence the velocity of grip closure in the way that one would expect if size were misperceived. Thus there is no reason to assume that the perceived size guides the way that we reach and grasp an object.     

How does action resist visual illusion? Uncorrected oculomotor information does not account for accurate pointing in peripersonal space

The amplitudes and signs of cutaneous reflexes are modulated during rhythmic movements of the arms and legs (during walking and arm or leg cycling for instance). This reflex modulation is frequently independent of the background muscle activity and may involve central pattern generator (CPG) circuits. The purpose of the present study was to investigate the nature and degree of coupling between the upper limbs during arm cycling, with regard to the regulation of cutaneous reflexes. Responses to electrical stimulations of the right, superficial radial nerve (five 1 ms pulses, 300 Hz) were recorded bilaterally in six arm muscles of eight participants during arm cycling involving only the limb ipsilateral to the stimulation, only the limb contralateral to the stimulation, and bilateral movement when the limbs were both in-phase and 180° out of phase. The pattern of cutaneous reflex modulation throughout the arm cycle was independent of the functional state of the limb contralateral to the recording site, irrespective of whether recordings were made ipsilateral or contralateral to the stimulation. Furthermore, cutaneous reflexes were significantly (p<0.05) modulated with arm position in only 8% of cases in which the limb containing the responding muscle was either stationary or being moved passively by the experimenter. The results show that there is relatively weak coupling between the arms with regard to the regulation of cutaneous reflexes during rhythmic, cyclical arm movements. This suggests a loose connection between the CPGs for each arm that regulate muscle activity and reflex amplitude during rhythmic movement.     

The Müller-Lyer illusion affects the planning and control of manual aiming movements

Participants made perceptual judgments about the length of, and manual aiming movements to the opposite end of, formerly visible Müller-Lyer stimuli. The Müller-Lyer illusion affected both perceptual judgments and aiming amplitude. Manipulations of stimulus duration (10 ms or 3000 ms) and memory delay length (10 ms or 3000 ms) had no impact on the illusory effect. Aiming movements executed with vision of the hand were less affected by the illusion than movements executed without vision of the hand. The effect of the illusion on aiming amplitude remained the same between peak velocity and the end of the movement even though participants were engaged in on-line control between peak deceleration and the end of the movement. This latter finding was counter to the predictions of a hypothesis (Glover 2002) stating that illusions should only affect the early (planning) stages of movement and not the late (control) stages of movement. We conclude that a single visual representation is used for perception, motor planning, and motor control.     

Expression of glycine receptor and transporter on bullfrog retinal Müller cells

The expression of the glycine receptor (GlyR) alpha1, alpha2 and beta subunits and glycine transporter (GlyT) on Müller cells was studied in bullfrog retina using double immunofluorescence labeling and confocal scanning microscopy. Double labeling of glial fibrillary acidic protein (GFAP), a specific marker for Müller cells, and the GlyR subunits showed that almost all Müller cells moderately expressed GlyR alpha1 and weakly GlyR beta, whereas no immunoreactivity for GlyR alpha2 was observed. The labeling for GlyR alpha1 and GlyR beta appeared in somata, major processes, endfeet and branchlets of the Müller cells. Müller cells were also GlyT1-labeled. Consistent with previous electrophysiological results, these findings suggest that Müller cells may be involved in modulation of glycinergic transmission by reciprocal interactions with retinal neurons through GlyR and GlyT.     

The effects of inverting prisms on the horizontal–vertical illusion: a systematic effect of downward gaze

The purpose of this work is to compare the relative contributions from the extraocular and sensory systems on the magnitude of the horizontal–vertical illusion (HVI). The visual HVI refers to the general tendency to overestimate vertical extensions of small-scale lines on a picture plane relative to the horizontal by 4–16% depending on the method of measurement. The HVI line stimuli consisted of luminous vertical and horizontal lines forming “L-profiles” located in the frontoparallel plane at a 45 cm viewing distance, collinearly with a binocular gaze. The home position of gaze was aligned to the center of the screen with the ear–eye angle concordant with the environmental horizontal. Illusion strength was quantified when subjects fixated the HVI line stimuli in four quadrants of the visual field. The HVI was also viewed through prism lenses that inverted the retinal images by 180°, thereby dissociating the sensory “up-down” direction from the oculomotor up-down frame of reference. The results revealed a systematically lower magnitude of the HVI in the bottom visual field regardless of whether subjects fixated the HVI with the distorting prisms or without. Taken together, these results suggest that the HVI is sensitive to small-angle gaze shifts. In agreement with several recent findings, these results are interpreted as implying that the brain imposes an enhanced analytic structure on the ascending sensory information during downward gaze. Hans O. Richter and Jaanus Raudsepp contributed equally to this work.     

The hand knows something that the eye does not: reaching movements resist the Müller-Lyer illusion whether or not the target is foveated

Previous reports suggest that saccades are affected by the Müller-Lyer (ML) pictorial illusion, whereas reaching movements are not. It is unclear if the resistance of reaching to illusions depends on the concurrent engagement of the oculomotor system. Here we show that the endpoints and kinematics of reaching movements were unaffected by a peripherally viewed ML stimulus regardless of whether or not a concurrent saccade was carried out. Primary saccade endpoints were affected by the ML stimulus but secondary saccades were not. Perceptual judgments of target location were influenced by the ML stimulus in the expected direction. The resistance of reaching movements to pictorial illusions does not appear to depend on the concurrent engagement of the oculomotor system. Implications for models of oculomotor and upper limb control are discussed.     

The integration of size and weight cues for perception and action: evidence for a weight–size illusion

Humans routinely estimate the size and weight of objects. Yet, when lifting two objects of equal weight but different size, they often perceive the smaller object as being heavier. This size–weight illusion (SWI) is known to have a lesser effect on motor control of object lifting. How the nervous system combines “weight” and “size” cues with prior experience and whether these cues are differentially integrated for perception and sensorimotor action is still not fully understood. Therefore, we assessed not only whether the experience of size biases weight perception, but also if experience of weight biases the size perception of objects. Further, to investigate differences between perceptual and motor systems for cue-experience integration, participants haptically explored the weight of an object with one hand and then shaped the aperture of their other hand to indicate its perceived size. Results—First, next to a SWI, healthy adults (N = 21) perceived lighter objects as being smaller and heavier objects as being larger, demonstrating a weight–size illusion (WSI). Second, participants were more susceptible to either the SWI or WSI. Third, aperture of the non-exploring hand was scaled to perceived weight and not to physical size. Hand openings were consistently smaller than physical size, with SWI-sensitive participants being significantly more affected than WSI-sensitive subjects. We conclude: first, both size and weight perceptions are biased by prior experience. Weight perception is biased by expectations of size, while size perception is influenced by the expectancy of weight. Second, humans have the tendency to use one cue predominantly for both types of perception. Third, combining perceived weight with expected size influenced hand motor control, while online haptic feedback was largely ignored. Finally, we present a processing model underlying the size–weight cue integration for the perceptual and motor system.     

Does an auditory perceptual illusion affect on-line auditory action control? The case of (de)accentuation and synchronization

Many recent studies have investigated whether visual (spatial) illusions affect visual (spatio-temporal) action control, with results that are far from simple. The present study asks the analogous question with regard to auditory temporal perception and action timing. The auditory illusion chosen for this particular study is the effect of increasing or decreasing the intensity of a tone in a sequence (i.e., accentuation or deaccentuation) on its perceived relative time of occurrence. The motor task is sensorimotor synchronization (finger tapping), specifically the automatic phase correction response to an advanced or delayed tone in a sequence. The strong hypothesis was that (de)accentuation would affect perceptual judgments of the tone's relative time of occurrence, but would have no effect at all on the phase correction response. The results of two experiments, if averaged across participants, confirm these predictions and furthermore suggest that individual perceptual and sensorimotor effects of (de)accentuation are uncorrelated. It is argued that perception and motor control in this case probably rely on different kinds of temporal information: relative versus absolute time of occurrence. Two unexpected findings complicate the results, however: the perceptual illusion was asymmetric, occurring only for delayed tones; and many individual participants did show significant differences in their phase correction response to accented and deaccented tones, although the direction of that difference varied.     

The effect of ACTH on the development of the athüs phenomenon and on the morphological composition of the inflammatory exudate

Summary Arthüs phenomenon was induced in 42 rabbits by the classical method. ACTH (10–20 units) was injected into 33 of them before the injection of the booster dose of horse serum, as well as beginning from the 3rd–4th administration of sensitizing doses. In the majority of experiments Arthüs phenomenon did not develop at all, or was much weaker than in control animals.The second group of experiments dealt with the cellular composition of the exudate in rats in experimental aseptic peritonitis caused by injecting sterile broth into the peritoneal cavity. Experimental results demonstrated that in animals which received ACTH (2.5 units) prior to broth injection the exudate was of thicker consistency and its cellular composition differed from control. Neutrophil percentage was much lower and lymphocytic phase occurred much earlier.The data obtained indicates the effect of ACTH both on the manifestation of allergic inflammation and on the exudative reaction during usual inflammation.(Presented by Active Member AMN SSSR P. S. Kupalov) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 55, No. 5, pp. 51–53, May, 1963     

Why two “Distractors” are better than one: modeling the effect of non-target auditory and tactile stimuli on visual saccadic reaction time

Saccadic reaction time (SRT) was measured in a focused attention task with a visual target stimulus (LED) and auditory (white noise burst) and tactile (vibration applied to palm) stimuli presented as non-targets at five different onset times (SOAs) with respect to the target. Mean SRT was reduced (i) when the number of non-targets was increased and (ii) when target and non-targets were all presented in the same hemifield; (iii) this facilitation first increases and then decreases as the time point of presenting the non-targets is shifted from early to late relative to the target presentation. These results are consistent with the time-window-of-integration (TWIN) model (Colonius and Diederich in J Cogn Neurosci 16:1000-1009, 2004) which distinguishes a peripheral stage of independent sensory channels racing against each other from a second stage of neural integration of the input and preparation of an oculomotor response. Cross-modal interaction manifests itself in an increase or decrease of second stage processing time. For the first time, without making specific distributional assumptions on the processing times, TWIN is shown to yield numerical estimates for the facilitative effects of the number of non-targets and of the spatial configuration of target and non-targets. More generally, the TWIN model framework suggests that multisensory integration is a function of unimodal stimulus properties, like intensity, in the first stage and of cross-modal stimulus properties, like spatial disparity, in the second stage.     

The effect of non–TNF-targeted biologics and small molecules on insulin resistance in inflammatory arthritis

Inflammatory arthritides are chronic diseases characterised by an increase in cardiovascular risk, largely attributable to the synergy between high-grade systemic inflammation and an elevated prevalence of traditional cardiovascular risk factors. Amongst the latter, insulin resistance and type 2 diabetes (T2D) play a key position. Previous studies demonstrated a potential insulin-sensitizing effect of anti-TNF biologic medications. For converse, less is known about the role of newer biologics or small molecules. For this reason, we performed a systematic review of the literature in order to identify the available data on the effect on insulin resistance of non-TNF targeting biologics and small molecules approved for the treatment of inflammatory arthritides. The search strategy initially retrieved 486 records of which only 10 articles were selected for inclusion in the final review. According to the available evidence, some of the newest molecules, in particular tocilizumab and abatacept, may have a role in improving insulin sensitivity; for converse, anakinra-mediated effect on glucose metabolism may exploit different facets of T2D pathophysiology, such as the preservation of beta-cell function. However, the data available on this issue are largely inconsistent and future, adequately designed studies are still needed to clarify the differential impact of novel therapeutics on individual pathophysiological features of T2D and other emerging cardiovascular risk factors.     

The electrophysiological effect of working memory load on involuntary attention in an auditory–visual distraction paradigm: an ERP study

Event-related brain potentials (ERPs) were used to examine the electrophysiological effect of working memory (WM) load on involuntary attention caused by a task-irrelevant sound in an auditory–visual distraction paradigm. The different WM loads were manipulated by requiring subjects to remember the order of either three digits (low-load condition) or seven digits (high-load condition), and the irrelevant auditory stimuli consisted of repetitive standard sounds (80%) and environmental novel sounds (20%). We found that the difference waves (novel-minus-standard) showed significant MMN and Novelty-P3 components in the two WM load conditions. The amplitude of MMN increased with increasing the WM load, which indicated a more engaged change detection process under high-load condition. Then, the amplitude of Novelty-P3 was attenuated under high-load condition, which indicated a much reduced involuntary orienting of attention to novel sounds when increasing the WM load. These results indicated the top–down control of involuntary attention might be mainly active at the early change detection stage and the control of the later involuntary orienting of attention might be passive.