When strangers pass: processing of mutual and averted social gaze in the superior temporal sulcus.

Using functional magnetic resonance imaging (fMRI), we investigated brain activity evoked by mutual and averted gaze in a compelling and commonly experienced social encounter. Through virtual-reality goggles, subjects viewed a man who walked toward them and shifted his neutral gaze either toward (mutual gaze) or away (averted gaze) from them. Robust activity was evoked in the superior temporal sulcus (STS) and fusiform gyrus (FFG). For both conditions, STS activity was strongly right lateralized. Mutual gaze evoked greater activity in the STS than did averted gaze, whereas the FFG responded equivalently to mutual and averted gaze. Thus, we show that the STS is involved in processing social information conveyed by shifts in gaze within an overtly social context. This study extends understanding of the role of the STS in social cognition and social perception by demonstrating that it is highly sensitive to the context in which a human action occurs.

Spatial and temporal scales of neuronal correlation in visual area V4.

The spiking activity of nearby cortical neurons is correlated on both short and long time scales. Understanding this shared variability in firing patterns is critical for appreciating the representation of sensory stimuli in ensembles of neurons, the coincident influences of neurons on common targets, and the functional implications of microcircuitry. Our knowledge about neuronal correlations, however, derives largely from experiments that used different recording methods, analysis techniques, and cortical regions. Here we studied the structure of neuronal correlation in area V4 of alert macaques using recording and analysis procedures designed to match those used previously in primary visual cortex (V1), the major input to V4. We found that the spatial and temporal properties of correlations in V4 were remarkably similar to those of V1, with two notable differences: correlated variability in V4 was approximately one-third the magnitude of that in V1 and synchrony in V4 was less temporally precise than in V1. In both areas, spontaneous activity (measured during fixation while viewing a blank screen) was approximately twice as correlated as visual-evoked activity. The results provide a foundation for understanding how the structure of neuronal correlation differs among brain regions and stages in cortical processing and suggest that it is likely governed by features of neuronal circuits that are shared across the visual cortex.

Frontal eye field neurons assess visual stability across saccades.

The image on the retina may move because the eyes move, or because something in the visual scene moves. The brain is not fooled by this ambiguity. Even as we make saccades, we are able to detect whether visual objects remain stable or move. Here we test whether this ability to assess visual stability across saccades is present at the single-neuron level in the frontal eye field (FEF), an area that receives both visual input and information about imminent saccades. Our hypothesis was that neurons in the FEF report whether a visual stimulus remains stable or moves as a saccade is made. Monkeys made saccades in the presence of a visual stimulus outside of the receptive field. In some trials, the stimulus remained stable, but in other trials, it moved during the saccade. In every trial, the stimulus occupied the center of the receptive field after the saccade, thus evoking a reafferent visual response. We found that many FEF neurons signaled, in the strength and timing of their reafferent response, whether the stimulus had remained stable or moved. Reafferent responses were tuned for the amount of stimulus translation, and, in accordance with human psychophysics, tuning was better (more prevalent, stronger, and quicker) for stimuli that moved perpendicular, rather than parallel, to the saccade. Tuning was sometimes present as well for nonspatial transaccadic changes (in color, size, or both). Our results indicate that FEF neurons evaluate visual stability during saccades and may be general purpose detectors of transaccadic visual change.

A pathway in primate brain for internal monitoring of movements.

It is essential to keep track of the movements we make, and one way to do that is to monitor correlates, or corollary discharges, of neuronal movement commands. We hypothesized that a previously identified pathway from brainstem to frontal cortex might carry corollary discharge signals. We found that neuronal activity in this pathway encodes upcoming eye movements and that inactivating the pathway impairs sequential eye movements consistent with loss of corollary discharge without affecting single eye movements. These results identify a pathway in the brain of the primate Macaca mulatta that conveys corollary discharge signals.

Reversible inactivation of macaque frontal eye field.

The macaque frontal eye field (FEF) is involved in the generation of saccadic eye movements and fixations. To better understand the role of the FEF, we reversibly inactivated a portion of it while a monkey made saccades and fixations in response to visual stimuli. Lidocaine was infused into a FEF and neural inactivation was monitored with a nearby microelectrode. We used two saccadic tasks. In the delay task, a target was presented and then extinguished, but the monkey was not allowed to make a saccade to its location until a cue to move was given. In the step task, the monkey was allowed to look at a target as soon as it appeared. During FEF inactivation, monkeys were severely impaired at making saccades to locations of extinguished contralateral targets in the delay task. They were similarly impaired at making saccades to locations of contralateral targets in the step task if the target was flashed for < or =100 ms, such that it was gone before the saccade was initiated. Deficits included increases in saccadic latency, increases in saccadic error, and increases in the frequency of trials in which a saccade was not made. We varied the initial fixation location and found that the impairment specifically affected contraversive saccades rather than affecting all saccades made into head-centered contralateral space. Monkeys were impaired only slightly at making saccades to contralateral targets in the step task if the target duration was 1000 ms, such that the target was present during the saccade: latency increased, but increases in saccadic error were mild and increases in the frequency of trials in which a saccade was not made were insignificant. During FEF inactivation there usually was a direct correlation between the latency and the error of saccades made in response to contralateral targets. In the delay task, FEF inactivation increased the frequency of making premature saccades to ipsilateral targets. FEF inactivation had inconsistent and mild effects on saccadic peak velocity. FEF inactivation caused impairments in the ability to fixate lights steadily in contralateral space. FEF inactivation always caused an ipsiversive deviation of the eyes in darkness. In summary, our results suggest that the FEF plays major roles in (1) generating contraversive saccades to locations of extinguished or flashed targets, (2) maintaining contralateral fixations, and (3) suppressing inappropriate ipsiversive saccades.

The acquisition of abstract words by young infants.

Young infants' learning of words for abstract concepts like 'all gone' and 'eat,' in contrast to their learning of more concrete words like 'apple' and 'shoe,' may follow a relatively protracted developmental course. We examined whether infants know such abstract words. Parents named one of two events shown in side-by-side videos while their 6-16-month-old infants (n=98) watched. On average, infants successfully looked at the named video by 10 months, but not earlier, and infants' looking at the named referent increased robustly at around 14 months. Six-month-olds already understand concrete words in this task (Bergelson & Swingley, 2012). A video-corpus analysis of unscripted mother-infant interaction showed that mothers used the tested abstract words less often in the presence of their referent events than they used concrete words in the presence of their referent objects. We suggest that referential uncertainty in abstract words' teaching conditions may explain the later acquisition of abstract than concrete words, and we discuss the possible role of changes in social-cognitive abilities over the 6-14 month period.

Peripheral ocular monochromatic aberrations

Aberrations affect image quality of the eye away from the line of sight as well as along it. High amounts of lower order aberrations are found in the peripheral visual field and higher order aberrations change away from the centre of the visual field. Peripheral resolution is poorer than that in central vision, but peripheral vision is important for movement and detection tasks (for example driving) which are adversely affected by poor peripheral image quality. Any physiological process or intervention that affects axial image quality will affect peripheral image quality as well. The aim of this study was to investigate the effects of accommodation, myopia, age, and refractive interventions of orthokeratology, laser in situ keratomileusis and intraocular lens implantation on the peripheral aberrations of the eye. This is the first systematic investigation of peripheral aberrations in a variety of subject groups. Peripheral aberrations can be measured either by rotating a measuring instrument relative to the eye or rotating the eye relative to the instrument. I used the latter as it is much easier to do. To rule out effects of eye rotation on peripheral aberrations, I investigated the effects of eye rotation on axial and peripheral cycloplegic refraction using an open field autorefractor. For axial refraction, the subjects fixated at a target straight ahead, while their heads were rotated by ±30º with a compensatory eye rotation to view the target. For peripheral refraction, the subjects rotated their eyes to fixate on targets out to ±34° along the horizontal visual field, followed by measurements in which they rotated their heads such that the eyes stayed in the primary position relative to the head while fixating at the peripheral targets. Oblique viewing did not affect axial or peripheral refraction. Therefore it is not critical, within the range of viewing angles studied, if axial and peripheral refractions are measured with rotation of the eye relative to the instrument or rotation of the instrument relative to the eye. Peripheral aberrations were measured using a commercial Hartmann-Shack aberrometer. A number of hardware and software changes were made. The 1.4 mm range limiting aperture was replaced by a larger aperture (2.5 mm) to ensure all the light from peripheral parts of the pupil reached the instrument detector even when aberrations were high such as those occur in peripheral vision. The power of the super luminescent diode source was increased to improve detection of spots passing through the peripheral pupil. A beam splitter was placed between the subjects and the aberrometer, through which they viewed an array of targets on a wall or projected on a screen in a 6 row x 7 column matrix of points covering a visual field of 42 x 32. In peripheral vision, the pupil of the eye appears elliptical rather than circular; data were analysed off-line using custom software to determine peripheral aberrations. All analyses in the study were conducted for 5.0 mm pupils. Influence of accommodation on peripheral aberrations was investigated in young emmetropic subjects by presenting fixation targets at 25 cm and 3 m (4.0 D and 0.3 D accommodative demands, respectively). Increase in accommodation did not affect the patterns of any aberrations across the field, but there was overall negative shift in spherical aberration across the visual field of 0.10 ± 0.01m. Subsequent studies were conducted with the targets at a 1.2 m distance. Young emmetropes, young myopes and older emmetropes exhibited similar patterns of astigmatism and coma across the visual field. However, the rate of change of coma across the field was higher in young myopes than young emmetropes and was highest in older emmetropes amongst the three groups. Spherical aberration showed an overall decrease in myopes and increase in older emmetropes across the field, as compared to young emmetropes. Orthokeratology, spherical IOL implantation and LASIK altered peripheral higher order aberrations considerably, especially spherical aberration. Spherical IOL implantation resulted in an overall increase in spherical aberration across the field. Orthokeratology and LASIK reversed the direction of change in coma across the field. Orthokeratology corrected peripheral relative hypermetropia through correcting myopia in the central visual field. Theoretical ray tracing demonstrated that changes in aberrations due to orthokeratology and LASIK can be explained by the induced changes in radius of curvature and asphericity of the cornea. This investigation has shown that peripheral aberrations can be measured with reasonable accuracy with eye rotation relative to the instrument. Peripheral aberrations are affected by accommodation, myopia, age, orthokeratology, spherical intraocular lens implantation and laser in situ keratomileusis. These factors affect the magnitudes and patterns of most aberrations considerably (especially coma and spherical aberration) across the studied visual field. The changes in aberrations across the field may influence peripheral detection and motion perception. However, further research is required to investigate how the changes in aberrations influence peripheral detection and motion perception and consequently peripheral vision task performance.

Changes in intraocular pressure and ocular pulse amplitude with accommodation

Aims: To investigate the change that occurs in intraocular pressure (IOP) and ocular pulse amplitude (OPA) with accommodation in young adult myopes and emmetropes. Methods: Fifteen progressing myopic and 17 emmetropic young adult subjects had their IOP and OPA measured using the Pascal dynamic contour tonometer. Measurements were taken initially with accommodation relaxed, and then following 2 min of near fixation (accommodative demand 3 D). Baseline measurements of axial length and corneal thickness were also collected prior to the IOP measures. Results: IOP significantly decreased with accommodation in both the myopic and emmetropic subjects (mean change 1.861.1 mm Hg, p<0.0001). There was no significant difference (p>0.05) between myopes and emmetropes in terms of baseline IOP or the magnitude of change in IOP with accommodation. OPA also decreased significantly with accommodation (mean change for all subjects 0.560.5, p<0.0001). The myopic subjects (baseline OPA 2.060.7 mm Hg) exhibited a significantly lower baseline OPA (p¼0.004) than the emmetropes (baseline OPA 3.261.3 mm Hg),and a significantly lower magnitude of change in OPA with accommodation. Conclusion: IOP decreases significantly with accommodation, and changes similarly in progressing myopic and emmetropic subjects. However, differences found between progressing myopes and emmetropes in the mean OPA levels and the decrease in OPA associated with accommodation suggested some changes in IOP dynamics associated with myopia.

Changes in ocular biometrics and refraction during near work in downward gaze over time

PURPOSE To investigate changes in the characteristics of the corneal optics, total optics, anterior biometrics and axial length of the eye during a near task, in downward gaze, over 10 min. METHODS Ten emmetropes (mean - 0.14 ± 0.24 DS) and 10 myopes (mean - 2.26 ± 1.42 DS) aged from 18 to 30 years were recruited. To measure ocular biometrics and corneal topography in downward gaze, an optical biometer (Lenstar LS900) and a rotating Scheimpflug camera (Pentacam HR) were inclined on a custom built, height and tilt adjustable table. The total optics of the eye were measured in downward gaze with binocular fixation using a modified Shack-Hartmann wavefront sensor. Initially, subjects performed a distance viewing task at primary gaze for 10 min to provide a "wash-out" period for prior visual tasks. A distance task (watching video at 6 m) in downward gaze (25°) and a near task (watching video on a portable LCD screen with 2.5 D accommodation demand) in primary gaze and 25°downward gaze were then carried out, each for 10 min in a randomized order. During measurements, in dichoptic view, a Maltese cross was fixated with the right (untested) eye and the instrument’s fixation target was fixated with the subject’s tested left eye. Immediately after (0 min), 5 and 10 min from the commencement of each trial, measurements of ocular parameters were acquired in downward gaze. RESULTS Axial length exhibited a significant increase with downward gaze and accommodation over time (p<0.05). The greatest axial elongation was observed in downward gaze with 2.5 D accommodation after 10 min (mean change from baseline 23±3 µm). Downward gaze also caused greater changes in anterior chamber depth (ACD) and lens thickness (LT) with accommodation (ACD mean change -163±12µm at 10 min; LT mean change 173±17 µm at 10 min) compared to primary gaze with accommodation (ACD mean change -138±12µm at 10 min; LT mean change 131±15 µm at 10 min). Both corneal power and total ocular power changed by a small but significant amount with downward gaze (p<0.05), resulting in a myopic shift (~0.10 D) in the spherical power of the eye compared with primary gaze. CONCLUSION The axial length, anterior biometrics and ocular refraction change significantly with accommodation in downward gaze as a function of time. These findings provide new insights into the optical and bio-mechanical changes of the eye during typical near tasks.

Ocular Reconstruction After Zygomatic Complex Fracture With Retention of a Foreign Body

Facial injuries with the retention of foreign bodies inside the tissues, both in soft and hard ones, can cause major functional and aesthetic damage. Among the different etiological agents, cutting tools, fragments of a firearm, the splinter of wood, steel, or iron, launched by misuse, or even caused by defects in equipment, are the main cause of these injuries. The aim of this study was to discuss the peculiarity of the multidisciplinary approach in caring of a 33-year-old man, victim of an accident at work, by the rupture of an emery disc and consequent penetration of the fragments in violation of the tissues in the orbital and zygomatic region of the left side, with perforation of the eyeball and orbital-zygomatic fracture. Urgent treatment consisted of debridement of wounds, bleeding control, removal of foreign bodies, fracture reduction with rigid internal fixation, and suture, performed by the oral and maxillofacial surgical team. Reconstruction of orbital tissues by the ophthalmology team consisted of suture of the injuries. About 1 month after the trauma, phthisis bulbi was noted, and the patient underwent a new procedure under general anesthesia for eye evisceration and installation of an alloplastic prosthesis associated with the homogenous sclera. Facial harmony was restored, especially in aesthetics and function of the zygomatic-orbital complex.

Minimally invasive strabismus surgery for rectus muscle posterior fixation

AIMS: To present a novel, minimally invasive strabismus surgery (MISS) technique for rectus muscle posterior fixation. METHODS: This study reports the results of 32 consecutive MISS rectus muscle posterior fixation surgeries performed on 19 patients by applying only two small L-shaped openings where the two retroequatorial scleromuscular sutures were placed. RESULTS: On the first postoperative day, in primary position, redness was hardly visible in 16 eyes (50%) and only moderate redness was visible in 6 eyes (19%). No serious complication occurred. Preoperative visual acuity and refraction remained unchanged at 6 months (p > 0.1). The preoperative convergence excess (n = 13) decreased from 10.3 +/- 4.1 to 5.2 +/- 4.0 degrees at 6 months (p < 0.005). In all patients operated on for gaze incomitance (n = 6) improvement was achieved at 6 months. CONCLUSIONS: This study shows that keyhole minimal-dissection rectus muscle posterior fixation surgery is feasible and effective to improve ocular alignment. The MISS technique seems to be superior in the direct postoperative period since only minimal conjunctival swelling and no corneal complications were observed.

Quantifying the vestibulo-ocular reflex with video-oculography: nature and frequency of artifacts

Video-oculography devices are now used to quantify the vestibulo-ocular reflex (VOR) at the bedside using the head impulse test (HIT). Little is known about the impact of disruptive phenomena (e.g. corrective saccades, nystagmus, fixation losses, eye-blink artifacts) on quantitative VOR assessment in acute vertigo. This study systematically characterized the frequency, nature, and impact of artifacts on HIT VOR measures. From a prospective study of 26 patients with acute vestibular syndrome (16 vestibular neuritis, 10 stroke), we classified findings using a structured coding manual. Of 1,358 individual HIT traces, 72% had abnormal disruptive saccades, 44% had at least one artifact, and 42% were uninterpretable. Physicians using quantitative recording devices to measure head impulse VOR responses for clinical diagnosis should be aware of the potential impact of disruptive eye movements and measurement artifacts.

The influence of fixation points on contrast detection and discrimination of patches of grating: Masking and facilitation

The use of fixation points (FPs) in visual psychophysics is common practice, though the costs and benefits of different fixation regimens have not been compared. Here we investigate the influence of several different types of FP configurations on the contrast detection of patches of sine-wave gratings. We find that for small targets (1°), the addition of a superimposed central FP can increase thresholds by a factor of 1.3 (2.5 dB) in comparison with no FP, and a factor of 1.5 (3.6 dB) in comparison with FPs that surround the target. These results are consistent with (i) a suppressive influence on the central region of the target from a central FP, and (ii) facilitatory influences from surrounding FPs. Our analysis of the slope of the psychometric function suggests that the facilitatory influence is not due to reduction of uncertainty. Plausible candidate causes for the facilitation are: (i) sensory interactions, (ii) aids to ocular accommodation and convergence, (iii) a reduction in eye-movements and (iv) more accurate placement of the observer’s window of attention. Masking by a central FP is not found for the suprathreshold task of contrast discrimination, suggesting that the masking effects of pedestal and FP do not combine linearly. This means that estimates of the level of masking produced by a contrast pedestal can depend on the details of the fixation point.