Tilt Discrimination Research Articles

Saccade execution increases the preview effect with faces: An EEG and eye-tracking coregistration study.

Under naturalistic viewing conditions, humans conduct about three to four saccadic eye movements per second. These dynamics imply that in real life, humans rarely see something completely new; there is usually a preview of the upcoming foveal input from extrafoveal regions of the visual field. In line with results from the field of reading research, we have shown with EEG and eye-tracking coregistration that an extrafoveal preview also affects postsaccadic visual object processing and facilitates discrimination. Here, we ask whether this preview effect in the fixation-locked N170, and in manual responses to the postsaccadic target face (tilt discrimination), requires saccade execution. Participants performed a gaze-contingent experiment in which extrafoveal face images could change their orientation during a saccade directed to them. In a control block, participants maintained stable gaze throughout the experiment and the extrafoveal face reappeared foveally after a simulated saccade latency. Compared with this no-saccade condition, the neural and the behavioral preview effects were much larger in the saccade condition. We also found shorter first fixation durations after an invalid preview, which is in contrast to reading studies. We interpret the increased preview effect under saccade execution as the result of the additional sensorimotor processes that come with gaze behavior compared with visual perception under stable fixation. In addition, our findings call into question whether EEG studies with fixed gaze capture key properties and dynamics of active, natural vision.

Intensity Discrimination and Speech Recognition of Cochlear Implant Users.

The relation between speech recognition and within-channel or across-channel (i.e., spectral tilt) intensity discrimination was measured in nine CI users (11 ears). Within-channel intensity difference limens (IDLs) were measured at four electrode locations across the electrode array. Spectral tilt difference limens were measured with (XIDL-J) and without (XIDL) level jitter. Only three subjects could perform the XIDL-J task with the amount of jitter required to limit use of within-channel cues. XIDLs (normalized to %DR) were correlated with speech recognition (r = 0.67, P = 0.019) and were highly correlated with IDLs. XIDLs were on average nearly 3 times larger than IDLs and did not vary consistently with the spatial separation of the two component electrodes. The overall pattern of results was consistent with a common underlying subject-dependent limitation in the two difference limen tasks, hypothesized to be perceptual variance (how the perception of a sound differs on different presentations), which may also underlie the correlation of XIDLs with speech recognition. Evidence that spectral tilt discrimination is more important for speech recognition than within-channel intensity discrimination was not unequivocally shown in this study. However, the results tended to support this proposition, with XIDLs more correlated with speech performance than IDLs, and the ratio XIDL/IDL also being correlated with speech recognition. If supported by further research, the importance of perceptual variance as a limiting factor in speech understanding for CI users has important implications for efforts to improve outcomes for those with poor speech recognition.

Impaired tilt perception in Parkinson's disease: a central vestibular integration failure.

IntroductionImpaired balance control is a hallmark symptom in Parkinson’s disease (PD). Altered sensory-motor integration contributes to the deficiency. We aimed to determine whether impaired vestibular signal processing added to the disorder. We exposed patients (N = 11; 68±6y) and age-matched healthy subjects (hS: N = 19; 65±11y) on a motion platform in complete darkness to two consecutive forward tilt movements (12 series; N = 24; overall 288 trials) and asked them to indicate which tilt was perceived larger. By combing tilt movements with translations we manipulated vestibular sensory input in order to investigate whether putative impairment resulted from a deficiency of the sensory organs (semicircular canals in ‘single-SCC-cue-condition’, otoliths in ‘single-OT-cue-condition’) themselves or to a sensory integration failure (‘multi-cue-condition’).ResultsTilt discrimination in the multi-cue-condition was inferior in patients compared to hS (p = 0.02). No significant differences between the two groups were found for both single-cue-conditions. Comparison of multi-cue-condition with a prediction resulting from the combination of both single-cue-conditions by optimal observer theory revealed that patients (p = 0.04), in contrast to hS, failed to efficiently combine SCC and OT information to improve tilt perception.ConclusionWe found that PD patients distinguished forward tilts less precise than hS, suggesting impaired vestibular perception. Tilt discrimination in patients, moreover, did not improve as much as in hS in conditions where both SCC and OT information was available compared to conditions where only SCC or OT cues were activated. The latter provides evidence that tilt misperception in PD most likely results from an integration failure of vestibular signals.

Adults with dyslexia demonstrate large effects of crowding and detrimental effects of distractors in a visual tilt discrimination task.

Previous research has shown that adults with dyslexia (AwD) are disproportionately impacted by close spacing of stimuli and increased numbers of distractors in a visual search task compared to controls [1]. Using an orientation discrimination task, the present study extended these findings to show that even in conditions where target search was not required: (i) AwD had detrimental effects of both crowding and increased numbers of distractors; (ii) AwD had more pronounced difficulty with distractor exclusion in the left visual field and (iii) measures of crowding and distractor exclusion correlated significantly with literacy measures. Furthermore, such difficulties were not accounted for by the presence of covarying symptoms of ADHD in the participant groups. These findings provide further evidence to suggest that the ability to exclude distracting stimuli likely contributes to the reported visual attention difficulties in AwD and to the aetiology of literacy difficulties. The pattern of results is consistent with weaker and asymmetric attention in AwD.

Allocation of attention across saccades

Whenever the eyes move, spatial attention must keep track of the locations of targets as they shift on the retina. This study investigated transsaccadic updating of visual attention to cued targets. While observers prepared a saccade, we flashed an irrelevant, but salient, color cue in their visual periphery and measured the allocation of spatial attention before and after the saccade using a tilt discrimination task. We found that just before the saccade, attention was allocated to the cue's future retinal location, its predictively "remapped" location. Attention was sustained at the cue's location in the world across the saccade, despite the change of retinal position whereas it decayed quickly at the retinal location of the cue, after the eye landed. By extinguishing the color cue across the saccade, we further demonstrate that the visual system relies only on predictive allocation of spatial attention, as the presence of the cue after the saccade did not substantially affect attentional allocation. These behavioral results support and extend physiological evidence showing predictive activation of visual neurons when an attended stimulus will fall in their receptive field after a saccade. Our results show that tracking of spatial locations across saccades is a plausible consequence of physiological remapping.

Three-dimensional retinal image stability during visual tilt discrimination in the rabbit

Rabbits trained to discriminate vertical vs. oblique striations are unable to discriminate angular differences of 5°. In the present study the instabilities around the roll axis of the eyes were measured during visual discrimination. The results indicate that these instabilities are one of the causes of the rabbit's inability to discriminate angular differences of 5°.

Tilt discrimination in the mouse

We tested the visual discrimination of mice in a two-choice discrimination box. After reaching criterion in a brightness discrimination the animals were trained on an orientation discrimination (vertical vs horizontal). Training was continued with the discrimination of vertical striations (S +) vs oblique ones (S −) of 10 different angles (80 to 15 degrees). The tilt discrimination for the last 5 days of training we found to be 30.5 (S.E.M. 3.2) degrees in albino and 19.9 (S.E.M. 0.7) degrees in pigmented mice. This is much higher than the 9.55 (S.E.M. 0.95) degrees found in pigmented rabbits but is comparable to the 17 degrees found in hooded rats by others.

Tilt discrimination in the albino mouse

Tilt discrimination in the albino mouse

Visual discrimination after early and late unilateral enucleation of the rabbit

Brightness and tilt discrimination were studied in rabbits in which one eye had been enucleated either 1 day or 3 months after birth. When tested at the age of 5 months no differences in performance were found between both groups of animals.

The accuracy of tilt discrimination in the rabbit

The accuracy with which rabbits are able to discriminate vertical and oblique lines was studied under circumstances in which the retinal patterns were optimally focussed. It was found that orientation discrimination breaks down with angular differences smaller than 10°.

Tilt discrimination after unilateral ablation of the occipital lobe in rabbits operated at adult age or immediately after birth

Tilt discrimination after unilateral ablation of the occipital lobe in rabbits operated at adult age or immediately after birth

An interval scale for measuring visual pattern discrimination of a mammal ( Rattus norvegicus)

Laboratory rats, trained to horizontal or vertical stripes, were scored on visual stripe tilt discrimination in a series of binary choice tests. The resulting choice-percent-scales can be shown to be linear measurements (interval scales) of the stripe tilt differences as perceived by the rats. A crude model system for describing and explaining the binary choice behavior of rats is propounded. Three main processes constitute this model system. The first determines the magnitude of similarity between any pattern offered and the previous training pattern. The second compares these similarity-magnitudes by subtraction and the third injects evenly distributed noise into the system, thus accounting for the scatter in the choice behavior. The similarity functions (“generalization gradients”) for the edge orientation in the visual field of the rat range over ± 90°, which appears to be typical for both vertebrates and arthropods.

Tilt discrimination and aftereffect with stroboscopic display of contours

Previous studies have shown that motion perception is degraded when the visual stimulus is stroboscopically illuminated. The present experiment indicated that the accuracy in discrimination of the orientation of an intermittently presented stationary grating is unaffected by flicker rate. In addition, the orientation aftereffect induced by successive display of a tilted and vertical grating is independent of the flicker rate of each stimulus. These results indicate that mechanisms engaged in neural representation of contour information are not conjointly sensitive to the rate of temporal intermittency within the visual display.

Pattern discrimination in rabbits deprived of light for 7 months after birth

Rabbits deprived of light for 7 months after birth and those raised normally were studied for pattern discrimination ability. Before the patterns were applied the animals were made cooperative in a training box. In the animals that had been deprived of light, this procedure took about twice as long as in the normal animals. The animals subsequently learned to discriminate horizontal vs vertical and 45 vs 135° striations. Thereafter the accuracy of tilt discrimination (various angle differences between vertical and oblique striations) was studied. No differences were found between the two groups. The same result was obtained when rows of dots were used instead of striations. Visual acuity on the other hand was found to be lower in animals that had been reared in the dark.

Visual discrimination of “unseen” objects: Forced-choice testing of Mayzner-TresseIt sequential blanking effects

Display elements were sequentially painted upon a display scope in regular and irregular spatial-temporal orders. The primary result of Mayzner, Tresselt, and their associates is confirmed: within specified temporal-spatial limits, display elements may be perceptually blanked. Characteristics of perceptually blanked elements can, however, be revealed by forced-choice testing. The accuracy of tilt discrimination for perceptually blanked elements is equal to, or better than, that for nonblanked elements. Perceptually blanked elements can also be distinguished from absent and from partially absent elements, presumably on the basis of a crude brightness discrimination. Sequential blanking effects as revealed in the accuracy of slant detection, are not critically dependent upon the magnitude of uniform spacing between the display elements.

SELECTIVE ATTENTION: THE EFFECTS OF COMBINING STIMULI WHICH CONTROL INCOMPATIBLE BEHAVIOR1

Four rhesus monkeys learned both a color and tilt discrimination. The stimuli were combined to produce incompatible behavior. The behavior controlled by one set of stimuli was reinforced until "errors" virtually disappeared. The stimuli were tested separately again. Sixteen replications of the entire procedure indicated that the stimuli producing "errors" were ignored.

Discrimination of striated patterns of different orientation in rabbits deprived of light after birth

Rabbits deprived of light during the first 6 weeks after birth and animals raised under normal conditions were trained to discriminate striations of different orientation at the age of 6 months. The ability to discriminate vertical vs. horizontal and 45 vs. 135° striations as well as the angular threshold of tilt discrimination was the same in both groups.

An observation on stimulus control in a tilt discrimination by children.

Most children who learned to discriminate opposing 45 degrees line tilts on a relational basis-oddity-did not learn the specific direction of the positive tilt. Most children who did not use oddity did discriminate the specific tilt.

THE COURSE OF ACQUISITION OF A LINE‐TILT DISCRIMINATION BY RHESUS MONKEYS1

Each of four groups of monkeys were trained on a different simultaneous discrimination procedure involving a vertical line as the correct choice. Each group, after acquiring the discrimination, was tested for generalization along the dimension of line tilt. Monkeys that learned to select the vertical line when the alternative choices were distinguished from the correct choice by two aspects (brightness and absence of line) showed almost complete tilt generalization (flat gradient). Monkeys that learned to select the line when the alternatives were distinguished only by the absence of the line showed poor tilt discrimination (generalization gradient slightly peaked at vertical). Monkeys developed a good tilt discrimination when nonvertical lines were gradually introduced by progressively darkening them on the previously blank alternatives. Monkeys developed a tilt discrimination with the lowest error rate when only horizontal alternatives were gradually introduced and then pairs of alternatives progressively closer to vertical were made available.

Visual areas I and II of cerebral cortex of rabbit.

Visual areas I and II of cerebral cortex of rabbit.