bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relevant Image Features for Vernier Acuity
Authors: Beard B L , Ahumada A J 
Published: December 2015

The extraction of relevant image features is a key part of discrimination learning (E Gibson, 1969 Principles of Perceptual Learning and Development) and the identification of those features is necessary for the understanding of observer performance. Two mechanisms are thought to limit Vernier acuity judgments: orientation-selective and local-sign mechanisms (Waugh and Levi, 1993 Vision Research33 539 – 552; Beard et al, 1997 Vision Research37 325 – 346). The linear component of relevant image features can be determined for a Vernier task by adding external noise to the image and then averaging the noises separately for the four types of stimulus/response trials. The Vernier stimulus consisted of two short, dark, horizontal lines presented within low-contrast white noise. Two spatial separations were tested: nearly abutting and a wide horizontal separation. The task was to determine if the target lines were aligned or offset in the vertical direction. The noises were averaged separately for the groups of trials, corresponding to each of the four possible stimulus/response combinations (eg, stimulus=offset, response=aligned). The sum of the two ‘not aligned’ images was then subtracted from the sum of the ‘aligned’ images to obtain an overall image. We then computed a weighted average of adjacent pixels, smoothing the image and fostering visualisation of the relevant feature pattern. Our image analysis supports the view that as the vernier line separation narrows, oriented features play a larger role in the Vernier discrimination.
Up-Down Asymmetries in Speed Perception
Authors: Thompson P , Stone L S 
Published: December 2015

We compared speed matches for pairs of stimuli that moved in opposite directions (upward and downward). Stimuli were elliptical patches (2 deg horizontally by 1 deg vertically) of horizontal sinusoidal gratings of spatial frequency 2 cycles deg−1. Two sequential 380 ms foveal presentations were compared. One of each pair of gratings (the standard) moved at 4 Hz (2 deg s−1), the other (the test) moved at a rate determined by a simple up - down staircase. The point of subjectively equal speed was calculated from the average of the last eight reversals. The task was to fixate a central point and to determine which one of the pair appeared to move faster. Eight of ten observers perceived the upward drifting grating as moving faster than a grating moving downward but otherwise identical. On average (N = 10), when the standard moved downward, it was matched by a test moving upward at 94.7± 1.7(SE)% of the standard speed, and when the standard moved upward it was matched by a test moving downward at 105.1± 2.3(SE)% of the standard speed. On extending this paradigm over a range of spatial (1.5 to 13.5 cycles deg−1) and temporal (1.5 to 13.5 Hz) frequencies, preliminary results (N = 4) suggest that, under the conditions of our experiment, upward motion is seen as faster than downward motion for speeds greater than ∼1 deg s−1, but the effect appears to reverse at speeds below ∼1 deg s−1 with downward motion perceived as faster. Given that an up - down asymmetry has been observed by other investigators for the optokinetic response, both perceptual and oculomotor contributions to this phenomenon deserve exploration.
Visual Acuity Affected by Size Perception Based on Convergence Cue
Authors: Shinoda H , Ikeda M 
Published: December 2015

Increasing (or decreasing) the convergence angle can shrink (or expand) the perceived size of an object without changing its retinal size (Oyama, 1974 Perception & Psychophysics16 175 – 182). Here we address the question whether such a change in perceived size affects visual acuity. We investigated the effects of perceived size on the legibility of letters, using a telestereoscope consisting of four mirrors to control the observer's convergence angle while keeping the size of the retinal image constant. The targets were photocopies of ordinary Japanese books containing both types of Japanese characters, kana and kanji. The former is a phonetic character and simpler than the latter. Letters were printed in black on white paper. First, we demonstrated that letters do become more legible (illegible) as perceived size expands (shrinks), although their retinal size does not change. Then, we measured the size of the convergence angle at which letters became legible. The ‘threshold’ size of the convergence angle was obtained for several retinal sizes (0.1 to 0.2 deg) of letters, and for kana and kanji, respectively. Four subjects participated in the experiment. The result shows that the threshold convergence angle for legibility decreases as the retinal size of letters decreases, so that the minimum retinal size of legible letters depends linearly on the convergence angle. The results implicate contributions from higher levels of the visual system to the determination of visual acuity.
Highly Accurate Measurements of Human Colour Vision Parameters with Application to Diagnostics
Authors: Chistopolov A V 
Published: December 2015

A new method for measuring a wide spectrum of parameters describing a subject's colour vision is presented. It is based on a portable visual colorimeter, ‘Spectr-3M’, designed in our laboratory and has several useful features: (1) it enables testing over a wide area of the chromaticity diagram; (2) it allows the use of continuously changing colour stimuli; (3) the measurement accuracy is high; (4) the testing procedure is fast and comfortable, minimising the effects caused by prolonged testing and increasing the reliability of the data. Using this method we have revealed significant deviations from the CIE 1931 standard colorimetric observer in the colour perception of several subjects previously attested by the Rabkin and Ishihara charts as having normal perception. The data obtained by our method are more informative than results obtained with the Nagel anomaloscope, revealing not only general features of colour perception defects (as the anomaloscope), but allowing more detailed characterisation, including even small deviations from the CIE 1931 standard observer.
Spatial Extent of Masking by Sine-Wave Gratings
Authors: Babenko V V 
Published: December 2015

The contrast threshold for detection of a target consisting of 1.5 periods of a sine wave was determined as a function of the number of cycles in a sinusoidal mask with the same spatial frequency and orientation. The test frequencies were 2, 4, and 8 cycles deg−1. The masks were spatial-frequency modulated so as to equate their spectral extent. Stimuli were seen monocularly in Maxwellian view at a mean luminance of 10 cd m−2. The contrast threshold in a backward masking paradigm was determined by a 2AFC staircase. Data were obtained from three subjects with normal vision. It was found that as the number of cycles in the mask was increased, the contrast threshold fell, but only to a certain level. The full range of the threshold decrement was about 2 dB. At all the spatial frequencies tested, the final threshold level was reached with 3 cycles in the mask and then remained unaffected by a further increase in the number of cycles. The results implicate frequency-tuned mechanisms of very restricted spatial extent. It is suggested that these may underlie processing of spatially distributed information at the post-striate stages.
Eye-Position Effects on the Visual Transfer Function
Authors: Bobrova-Evpiatieva E V 
Published: December 2015

Light responses of neurons in several brain areas are affected by eye position (Andersen et al, 1990 Journal of Neuroscience10 1176 – 1196). To find out if eye position may influence contrast sensitivity, measurements were made of the spatial contrast modulation transfer function at two different eye positions: with the gaze directed straight ahead and horizontally deflected by 30 deg, respectively. Eleven gratings (1.05 – 36.8 cycles deg−1) were presented so that their retinal position was identical at both eye positions. The data obtained show a significant effect of eye position on contrast sensitivity in 4 subjects out of 8. We found a mean decrease in contrast sensitivity by 10.8% in the ‘deflected’ condition. The eye-position effect was pronounced at low (14.8%) and high (29.6%) frequencies, being insignificant at middle frequencies. The maximal sensitivity decrease observed was 62.1% at 25 cycles deg−1 in one subject. In 4 of the subjects, no significant eye-position effect was found. Thus a horizontal deflection of the gaze direction can narrow the visual transfer function in some observers and consequently impair perception of near-threshold objects dominated by high or low spatial frequencies. Further studies will show what may account for this phenomenon: the interaction of retinal and eye position signals and/or optical changes due to compression of the eye ball.
Accuracy of Pointing to Invisible Landmarks in a Familiar Environment
Authors: Sellen K , van Veen H A H C , Bülthoff H H 
Published: December 2015

Humans develop a mental representation of their environment that enables them to solve their day-to-day navigation tasks. The nature and quality of this representation can be probed experimentally by studying spatial tasks like distance and bearing estimation. We investigated pointing accuracy in an outdoor environment as part of a larger project in which we compare spatial behaviour in real environments with that in virtual environments (virtual reality). We carried out experiments in the centre of Tübingen (ca 600 m × 400 m). Standing near one of eleven well-known landmarks, subjects had to turn a pointer in the estimated direction of each of the other ten invisible (occluded) landmarks (all ten subjects had lived in Tübingen for at least two years). The estimated directions were read by the experimenter from a hidden compass and later compared with the actual directions. This procedure was repeated from all eleven locations along the subjects' route through the town. The mean absolute angular error of pointing was 10.8°, while the individual subject's means ranged from 9.1° to 15.0°. We found highly significant differences in pointing accuracy for the different locations; mean absolute error ranged from 6.3° to 15.8° ( n=10). Systematic asymmetries in pointing from one landmark to another and back were not found. The pointing accuracy found in this study is clearly better than that found in most other studies, which might relate to the familiarity and the size of the environment. The apparent absence of an asymmetry in the pointing directions between two locations is consistent with the notion of a metric mental map.
Influence of Scanning Eye Movements on the Scintillating-Grid Illusion
Authors: Böhm S G , Schrauf M , Wölwer W , Wist E R 
Published: December 2015

The scintillating grid is an example of a brightness contrast illusion in which bright disks are superimposed on a Hermann grid. Dark spots are perceived within the bright disks as flashing with each flick of the eye (Schrauf et al Vision Research in press). With steady fixation, stimulation must be brief for the illusion to occur. Varying exposure duration with steady fixation, we found the maximum illusion at durations between 210–350 ms (Schrauf et al, 1996 Perception25 Supplement, 78). In the present study voluntary saccadic eye movements were used to produce brief exposures during fixations. The task of 5 trained subjects was to scan scintillation grids of five different spacings (0.5 – 2.0 deg separation of grid elements, observation time 60 s) in a manner yielding a maximum scintillating effect. Eye movements were recorded binocularly at 100 Hz with the Demel Debic 90 infrared corneal reflection tracker (resolution: 6 min arc). For each fixation we calculated latency and position. Durations and amplitudes of the saccades increased with decreasing angular separation of grid elements. When the illusion was maximal, roughly 60% of fixation durations were between 250 and 550 ms. These durations overlap with those obtained with steady fixation combined with variable exposure durations. Unlike the Hermann grid illusion, where illusory dark spots can be perceived at very brief exposure durations, the scintillating grid illusion takes much more time to develop. The long optimal durations found here are discussed in relation to mechanisms of scanning eye movements.
Altered Functions of Visual Brain Areas: Review of Recent Evidence from Blind Human Subjects
Authors: Kujala T , Alho K 
Published: December 2015

We investigated the functional role of human visual brain areas deprived of visual information. To this end, we recorded brain activity elicited by auditory and somatosensory stimuli in blind human subjects. Activity was recorded in the ‘Attend’ condition, in which subjects detected occasional deviant stimuli presented among repetitive standard stimuli and in the ‘Ignore’ condition, in which subjects did not attend to the stimuli. The results indicate that in the early-blinded subjects, event-related potential (ERP) topography elicited by deviant auditory and somatosensory target stimuli is posterior to that in the sighted (Kujala et al, 1995 Experimental Brain Research104 519 – 526). This suggests involvement of posterior brain areas in auditory and somatosensory processing in the blind humans. For the auditory modality, activated areas were located with magnetoencephalography (MEG), which indicates involvement of extrastriate occipital areas in detection of auditory targets (Kujala et al, 1995 Experimental Brain Research103 143 – 146). Visual-cortex plasticity was further studied in subjects who had lost their vision after childhood in order to clarify whether these cross-modal changes are specific to visual deprivation of early onset. In that study, auditory ERP topographies of late-blinded, early-blinded, and sighted subjects were compared. Comparison of posterior topography of ERPs elicited by deviant target stimuli in both early-blinded and late-blinded subjects with that in the sighted subjects suggests visual-cortex involvement in auditory processing even in late-onset blindness (Kujala et al, 1977 Psychophysiology34 213 – 216). Preliminary MEG recordings in one late-blinded subject provided further support for posterior generators (parietal-occipital) in auditory processing.
Spatial-Frequency Characteristics of Different Areas of Human Cortex
Authors: Harauzov A K , Shelepin Y E , Pronin S V 
Published: December 2015

We recorded visual evoked potentials in normal subjects from different areas of the occipital cortex, from the temporal and parietal lobes according to the ‘ten - twenty’ electrode system. Stimuli were black-and-white sine-wave gratings with eight different spatial frequencies in the range 0.45 to 14.4 cycles deg−1, presented at four different temporal frequencies (1, 2, 4, 8 Hz). Stimulation was either contrast-reversal or onset. VEPs were analysed both by component analysis and by Fourier transformation. Spatial characteristics were measured from the dependence of the amplitudes and latencies of the main response components (N1, P1, N2, P2) on the contrast and spatial frequency of the gratings. The characteristics obtained in the occipital lobe are in accordance with earlier experimental data [Regan, 1989 Human Electrophysiology (Amsterdam: Elsevier)]. When the temporal frequency of stimulation was increased, the maximum of the spatial-frequency curves shifted to lower spatial frequencies. However, we found differences in the spatial-frequency characteristics of different cortical areas. The results are discussed in terms of differences in the spatial and temporal tuning of the receptive fields of neurons in these areas.
Task-Dependence of Texture-Segregation-Specific VEP Components
Authors: Meigen T 
Published: December 2015

Recently, texture-segregation-specific components have been isolated in the human visual evoked potential (tsVEPs). As tsVEPs are characterised by a negative peak near 200 ms they occur between luminance-contrast responses (P100) and cognitive responses (P300). The aim of this study was to estimate the temporal overlap of tsVEPs and cognitive VEP components by directing a task to either visual or auditory stimuli. Eight visually normal subjects participated in the experiment. Horizontal and vertical line segments were arranged to yield either an ‘orientation chequerboard’ stimulus or two fields with homogeneous orientations. As auditory stimuli, two tones with different pitches were presented through headphones. Auditory and visual stimuli were temporally uncorrelated, which allowed off-line isolation of VEPs and AEPs by appropriate averaging from the same raw data. VEPs and AEPs were recorded from an array of 13 electrodes ranging from frontal to occipital positions. tsVEPs were isolated under two conditions, where the subjects detected the presence of (a) the orientation chequerboard, or (b) the higher pitch by pressing a button. It was found that (1) tsVEPs could be isolated under both tasks; (2) tsVEPs were strongly modulated by the task; (3) the task-specific modulation occurred in the same time domain as the tsVEP itself, but showed a different topography; (4) AEPs were less modulated by the task. The data suggest that an additional task concerning the gradient content of texture stimuli may modulate the resulting tsVEPs. This may partially account for the interindividual variability in recent tsVEP data, as a comparable task may be introduced tacitly by the subjects.
Implication of the Yellow Pigment in Dichoptic Colour Mixing
Authors: de Mattiello M L F , Biondini A R , Salinas H 
Published: December 2015

Working with colours generated from the three primaries, we found earlier that blue made it difficult to obtain dichoptic mixtures, producing chromatostereopsis and alternation effects which disappeared with increasing eccentricity (1 deg 3 min) or decreasing intensity of the blue component. The unanswered question was: is it true that mixtures with a strong blue component can never be obtained centrally as some authors claim? Therefore, we returned to this subject, using the same methodology and analysing the role that the yellow pigment (YP) would play. First, the samples that previously produced the aforementioned effects were tested, confirming that chromatostereopsis stopped before the alternation. Immediately after that, identical samples were observed through low-density yellow filters that were superposed until both effects ceased. Since the density of the YP of the four participating observers had been previously measured, it was possible to calculate the necessary increase for each one of them, observing that the increment became smaller as the mixtures were displaced towards longer wavelengths. This behaviour indicates a possible function of YP: the attenuation of the blue cone signal to make it compatible with signal from the red and green cones. As the YP varies among observers, this might be the reason why some sources mention that these mixtures can be obtained. If this hypothesis is accepted, this should not be interpreted as a variation in the number of blue receptors through the macula, a variation not necessarily observed in physiology.
The MacKay Phenomenon: Is it All Hand-Waving?
Authors: Smith C , Lee B 
Published: December 2015

When a table-tennis bat with a light-bulb in its centre is waved about by another person in a stroboscopically lit room, the light appears to float free from the bat, although it is physically fixed. A related phenomenon was reported originally by MacKay [1958 Nature (London)180 507 – 508)]. This illusion disappears in an active condition, where observers move the bat with their own hands, which suggests a proprioceptive basis for the illusion. In our implementation with a Power Macintosh computer, the illusion occurred in both conditions. Thus ‘hand-waving’ is not inherent to the illusion but may exert its effect indirectly by promoting predictive eye-tracking movements. To test the hypothesis that the perceived position of the bulb is extrapolated between a visual icon, tied to retinal coordinates, and its actual physical location thus causing the displace-ment illusion, we performed two experiments. From experiment 1 we found that for simple one-dimensional movement, the displacement illusion occurs only when there is a change in direction such that the bulb appears to ‘overshoot’ the bat. In experiment 2, using random two-dimensional movement, we manipulated the length of the dark (non-visible) period. The overshoot increased from around 30 min arc at 65 ms to around 60 min arc at 300 ms. For longer dark periods (up to 2000 ms), the illusion occurred providing the change in direction was within the 300 ms window after stimulus offset. These results show that during discontinuous illumination, perceived location is determined by extrapolation.
Can Slip of the Retinal Image Cause Amblyopia?
Authors: Leinonen M T , Rinne P 
Published: December 2015

One of the main purposes of the oculomotor system is to keep the image projected on the retina stationary in spite of the continuous movement of the head. If the vestibulo-ocular and optokinetic reflexes are defective, the retinal image becomes blurred owing to the uncoordinated movements of the head and the eyes. It is well known that in children retinal blur caused by media opacities or large refraction errors results in amblyopia. In a similar way amblyopia could be caused by slip of the retinal image due to a defective oculomotor system. Our patient was a small for gestational age A-twin. He developed dystonic diplegia with poor head control. At the age of 7 months he was considered to have cortical visual impairment. In a magnetic resonance image of the brain there were diffuse periventricular changes in the white matter and hypoplasia of the corpus callosum and the cerebellar vermis. Binocular optokinetic reflexes to full-field stimuli were horizontally asymmetric and were missing vertically. The reflexes to rotation of the child were asymmetric in the same way. In order to stabilise the retinal image the head of the child was supported always when he was supposed to look at a target with fine details. Increase in visual acuity measured with a Teller acuity card procedure was apparent after head support. This suggests that retinal slip can cause amblyopia. It is usual practice not to support the head of a child who has cerebral palsy and poor head control. In the case of defective head - eye coordination this practice could be harmful to the normal development of vision.