Treatment of Severe Pincer-Type Femoroacetabular Impingement With Arthroscopic Significant Acetabular Rim Correction and Circumferential Labral Reconstruction Improves Patient-Reported Outcome Measures.

PURPOSE: To validate an arthroscopic approach for performing significant acetabular rim correction and circumferential labral reconstruction required to treat severe pincer-type femoroacetabular impingement. METHODS: Using a minimum of 2-year follow-up, data from 48 hips, including 47 patients (11 male, 36 female; mean age of 42 years) having undergone significant arthroscopic acetabuloplasty for severe pincer impingement (center edge angle >45°) with concomitant circumferential allograft labral reconstruction were analyzed to determine improvements in patient-reported outcomes and degree of radiographic correction. RESULTS: Findings demonstrated a 98% success rate, including substantial improvements on all radiographic measurements and patient-reported outcomes. Minimal clinically important differences were met with extremely strong measures of effect. The mean center edge angle improved from 49° to 36° (MΔ = 13.96, P ≤ .001, standard deviation [SD] = 55.97, confidence interval [CI] 12.17- 15.62, d = 2.33) and the mean Tönnis angle improved from -6° to 0° (MΔ = 6.2, P ≤ .001, SD = 2.76 CI -7.1 to -5.39, d = 2.29). Modified Hip Harris Scores improved by a mean of 34.45 points (P ≤ .001, SD = 20.64, 95% CI 28.45-40.44, d = 1.66). Lower extremity functional scale scores improved by a mean of 27.35 points (P ≤ .001, SD = 18.37, 95% CI 22.02-32.69, d =1.48). No complications were reported. One case converted to a total hip arthroplasty (2%). CONCLUSIONS: Findings validated that the significant acetabular rim correction required to treat severe pincer morphology is safe and feasible via an arthroscopic approach. This, in addition to concomitant circumferential allograft labral reconstruction, resulted in improvement in patient-reported outcomes and radiographic measurements. LEVEL OF EVIDENCE: Level IV, therapeutic case-series.

Pupillary responses to differences in luminance, color and set size.

The pupil responds to a salient stimulus appearing in the environment, in addition to its modulation by global luminance. These pupillary responses can be evoked by visual or auditory stimuli, scaled with stimulus salience, and enhanced by multisensory presentation. In addition, pupil size is modulated by various visual stimulus attributes, such as color, area, and motion. However, research that concurrently examines the influence of different factors on pupillary responses is limited. To explore how presentation of multiple visual stimuli influences human pupillary responses, we presented arrays of visual stimuli and systematically varied their luminance, color, and set size. Saliency level, computed by the saliency model, systematically changed with set size across all conditions, with higher saliency levels in larger set sizes. Pupillary constriction responses were evoked by the appearance of visual stimuli, with larger pupillary responses observed in larger set size. These effects were pronounced even though the global luminance level was unchanged using isoluminant chromatic stimuli. Furthermore, larger pupillary constriction responses were obtained in the blue, compared to other color conditions. Together, we argue that both cortical and subcortical areas contribute to the observed pupillary constriction modulated by set size and color.

Superior colliculus encodes visual saliency before the primary visual cortex.

Models of visual attention postulate the existence of a bottom-up saliency map that is formed early in the visual processing stream. Although studies have reported evidence of a saliency map in various cortical brain areas, determining the contribution of phylogenetically older pathways is crucial to understanding its origin. Here, we compared saliency coding from neurons in two early gateways into the visual system: the primary visual cortex (V1) and the evolutionarily older superior colliculus (SC). We found that, while the response latency to visual stimulus onset was earlier for V1 neurons than superior colliculus superficial visual-layer neurons (SCs), the saliency representation emerged earlier in SCs than in V1. Because the dominant input to the SCs arises from V1, these relative timings are consistent with the hypothesis that SCs neurons pool the inputs from multiple V1 neurons to form a feature-agnostic saliency map, which may then be relayed to other brain areas.

Editorial Commentary: No Longer a Salvage Procedure: Allograft Labral Reconstruction of the Hip Rivals the Results of Labral Repair.

In the past 5 years, arthroscopic labral reconstruction of the hip has rapidly evolved from a salvage procedure used primarily in the setting of multiple failed prior hip surgical procedures to an alternative, and even preferable, primary treatment option for labral pathology and femoroacetabular impingement. As opposed to labral repair, labral reconstruction allows for complete removal of all damaged, pain-generating tissue; optimal correction of underlying bony impingement; and consistent creation of a graft that appropriately restores the fluid hip seal, improves pressurization and stabilization, and decreases contact pressure. Allograft tissue, in particular, allows for accurate and reliable graft length creation and does not rely on native tissue quality. Hips that undergo labral reconstruction have been shown to have positive outcomes at minimum 2-year follow-up, despite the fact that in many cases, these hips have more damage and a poorer preoperative prognosis. Patients report decreased pain, increased function, and greater quality of life after labral reconstruction, and this new evidence suggests that they can resume high-level physical activity as well. Circumferential labral reconstruction is no longer a salvage procedure and is an important tool for the hip arthroscopist; however, it requires high proficiency in hip arthroscopy to perform.

Hip Arthroscopy in Patients Aged 40 Years and Older: Greater Success With Labral Reconstruction Compared With Labral Repair.

PURPOSE: To assess the outcomes of complete, primary, arthroscopic hip labral reconstruction among patients aged 40 years and older compared with those who underwent primary labral repair and compared with patients aged 30 to 39 years who underwent complete, primary labral reconstruction. METHODS: We recruited all patients who underwent arthroscopic labral reconstruction between March 2010 and June 2015 and were aged 30 to 65 years or who underwent arthroscopic labral repair between June 2009 and June 2015 and were aged 40 to 65 years. The modified Harris Hip Score (mHHS), Lower Extremity Function Score, and visual analog scale score for average pain were collected preoperatively and at minimum 2-year follow-up. Failure was defined as the need for revision ipsilateral hip surgery. The rate of conversion to total hip arthroplasty (a subset of failure) was assessed separately. RESULTS: A total of 363 hips in 343 patients met the inclusion criteria. Follow-up was available for 312 hips (86.0%), and the average time to follow-up was 4.2 years (range, 2.0-8.5 years). After adjustment for differences in follow-up time between groups, failure was 3.29 times more likely for hips in the repair group aged 40 years and older than for hips in the reconstruction group aged 40 years and older (relative rate, 3.29; 95% confidence interval, 1.25-8.69; P = .02), and there was no difference in the failure rate for hips in the reconstruction group aged 40 years and older compared with hips in the reconstruction group aged 30 to 39 years (relative rate, 0.58; 95% confidence interval, 0.18-1.89; P = .37). The rate of conversion to total hip arthroplasty was not meaningfully different between the 3 groups. Among hips for which treatment did not fail, average improvement in the mHHS measured 35 points and both labral reconstruction groups saw a greater mHHS improvement than the labral repair group of patients aged 40 years and older (P = .01 and P < .01). CONCLUSIONS: Labral reconstruction led to a lower failure rate, greater average improvement in the mHHS, and equivalent postoperative patient-reported outcome scores compared with labral repair among patients aged 40 years and older in this study population, and the outcomes of labral reconstruction were similar between patients aged 40 years and older and those aged 30 to 39 years. Complete labral reconstruction may be particularly advantageous in patients aged 40 years and older. LEVEL OF EVIDENCE: Level III, retrospective comparative study.

Superior colliculus encodes visual saliency during smooth pursuit eye movements.

The saliency map has played a long-standing role in models and theories of visual attention, and it is now supported by neurobiological evidence from several cortical and subcortical brain areas. While visual saliency is computed during moments of active fixation, it is not known whether the same is true while engaged in smooth pursuit of a moving stimulus, which is very common in real-world vision. Here, we examined extrafoveal saliency coding in the superior colliculus, a midbrain area associated with attention and gaze, during smooth pursuit eye movements. We found that SC neurons from the superficial visual layers showed a robust representation of peripheral saliency evoked by a conspicuous stimulus embedded in a wide-field array of goal-irrelevant stimuli. In contrast, visuomotor neurons from the intermediate saccade-related layers showed a poor saliency representation, even though most of these neurons were visually responsive during smooth pursuit. These results confirm and extend previous findings that place the SCs in a unique role as a saliency map that monitors peripheral vision during foveation of stationary and now moving objects.

Bilateral Hip Arthroscopy: Direct Comparison of Primary Acetabular Labral Repair and Primary Acetabular Labral Reconstruction.

PURPOSE: Directly compare primary acetabular labral repair versus primary acetabular labral reconstruction using a self-controlled cohort study design. METHODS: Patients who underwent primary labral repair in one hip and primary labral reconstruction using iliotibial band allograft in the other hip by a single surgeon between August 2009 and November 2014 were identified. One patient with inflammatory arthritis was excluded. Patient-reported outcome data included change in Modified Harris Hip Score (MHHS), Lower Extremity Functional Scale (LEFS), average pain using a 10-point visual analog scale (VAS), and patient satisfaction (1: very dissatisfied, 10: very satisfied). Failure was defined as subsequent intra-articular hip surgery. Data were analyzed using McNemar's and Wilcoxon Signed Rank tests. RESULTS: Overall, 29 patients (58 hips) were included in the analysis. There were 23 females and 6 males. The average age at time of surgery was 32.6 years (range: 14.9-51.6 years). Follow-up was obtained from all 29 patients (100%) at a mean of 56 months (range = 27-85 months) postoperative for repaired hips and 40 months (range = 22-61 months) postoperative for reconstructed hips. No labral reconstruction hips failed, and 9 (31%) labral repair hips failed (P < .01). Among those that did not fail treatment, there was no difference in MHHS change (32.2 ± 15.4 vs 29.6 ± 15.4; P = .63), LEFS change (26.6 ± 16.5 vs 23.9 ± 17.8; P = .61), VAS pain change (-3.2 ± 2.4 vs -3.6 ± 2.1; P = .47), or satisfaction (8.6 ± 2.0 vs 8.7 ± 2.4; P = .59) between the repair and reconstruction groups, respectively. CONCLUSIONS: In this cohort of patients, hips that underwent primary labral repair were more likely to fail treatment than hips that underwent labral reconstruction (31% vs 0%, respectively). Among hips that did not fail treatment, patient-reported outcome scores were similar between groups. Excellent clinical results can be obtained with both forms of labral-preserving treatment but were more predictably observed with primary labral reconstruction in this cohort. LEVEL OF EVIDENCE: Level III, retrospective comparative study.

Revision Arthroscopic Acetabular Labral Treatment: Repair or Reconstruct?

PURPOSE: To compare the outcome of labral repair versus labral reconstruction in patients presenting to a single surgeon for revision hip arthroscopy following previous labral treatment. METHODS: Patients who underwent revision labral repair or labral reconstruction using iliotibial band allograft, after previous labral debridement or repair, between 2009 and 2013 were identified. Hips that underwent revision labral reconstruction were further stratified into 2 graft groups (freeze-dried vs frozen allograft). Exclusion criteria were age <16 years, previous open hip surgery, or previous labral reconstruction. Failure was defined by subsequent intra-articular hip surgery. RESULTS: 113 hips (15 repair, 98 reconstruction) met the inclusion criteria. Patients who underwent revision labral repair were younger than patients who underwent revision labral reconstruction (27.8 years vs 34.6 years; P = .02). Follow-up was obtained from 14 (93%) labral repairs at an average of 4.7 years postoperation (range: 2.0-6.0 years) and 90 (92%) labral reconstructions at an average of 2.4 years postoperation (range: 2.0-4.0 years). Seven of 14 (50%) labral repair hips failed compared with 11/90 (12%) labral reconstruction hips (P < .01). Six of 61 (10%) frozen allografts failed compared with 5/29 (17%) freeze-dried allografts (P = .32). Patients who underwent revision labral repair were 4.1 (95% confidence interval 1.9, 8.8) times more likely to fail than patients who underwent revision labral reconstruction. CONCLUSIONS: Patients who underwent revision labral repair following previous repair or debridement were 2.6 times more likely to fail than patients who underwent revision labral reconstruction, controlling for calendar time. In addition, revision labral reconstruction with frozen allograft had lower propensity of failure than freeze-dried allograft. However, there was no statistically significant difference in patient-reported outcome scores between the 2 groups. Based on these results, complete labral reconstruction with longer, nonsegmental graft led to a lower failure rate in this study population and can be considered for treatment of patients presenting for revision labral treatment. LEVEL OF EVIDENCE: Level III, retrospective comparative study.

Allograft Use in Arthroscopic Labral Reconstruction of the Hip With Front-to-Back Fixation Technique: Minimum 2-Year Follow-up.

PURPOSE: To present minimum 2-year outcomes in patients who underwent a modified technique for arthroscopic labral reconstruction using iliotibial band allograft tissue and a front-to-back fixation. METHODS: From April 2011 to July 2012, all consecutive arthroscopic labral reconstruction patients were included in this Institutional Review Board-approved, prospective case series study. Inclusion criteria were arthroscopic iliotibial band allograft labral reconstruction performed by a single surgeon, age ≥16 years at the time of arthroscopy, and a minimum of 2 years of follow-up. Patients completed subjective questionnaires both preoperatively and postoperatively, including Modified Harris Hip Score (MHHS), the Lower Extremity Function Score (LEFS), Visual Analogue Scale (VAS) pain scores, and patient satisfaction. A modified front-to-back fixation technique for labral reconstruction was used. RESULTS: One hundred fifty-two hips (142 patients) met the inclusion criteria for this study; 131 hips (86.2%) had complete follow-up at a minimum of 2 years, and 21 hips (13.8%) were lost to follow-up or had incomplete data during the study period. Seventy hips had concomitant procedures performed; 27 microfracture, 30 chondroplasty, 26 psoas release, 5 os acetabuli resection, and 3 Ganz osteotomy. Overall, 18 hips (13.7%) required revision procedures at a mean of 17 months (range, 1 to 37 months) after the labral reconstruction. In the remaining 113 hips, there was significant improvement in all outcome measures from preoperative to most recent follow-up (P < .0001). The mean MHHS improved by 34 points (P < .0001), and the mean LEFS improved by 27 points (P < .0001). The mean VAS pain score improved by 3 points at rest (P < .0001), 4 points with average pain with daily activities (P < .0001), and 5 points with sport (P < .0001). Patients reported an overall satisfaction of 9 (range, 1 to 10). CONCLUSIONS: Arthroscopic iliotibial band allograft labral reconstruction of the hip shows promising outcomes at minimum 2-year follow-up. LEVEL OF EVIDENCE: Level IV, therapeutic case series.

Spatio-temporal response properties of local field potentials in the primate superior colliculus.

Local field potentials (LFPs) are becoming increasingly popular in neurophysiological studies. However, to date, most of the knowledge about LFPs has been obtained from cortical recordings. Here, we recorded single unit activity (SUA) and LFPs simultaneously from the superior colliculus (SC) of behaving rhesus monkeys. The SC is a midbrain structure that plays a central role in the visual orienting response. Previous studies have characterised the visual and visuomotor response properties of SUA in the superficial layers of the SC and the intermediate layers of the SC, respectively. We found that the signal properties of SUA were well preserved in the LFPs recorded from the SC. The SUA and LFPs had similar spatial and temporal properties, and the response properties of LFPs differed across layers, i.e. purely visual in the superficial layers of the SC but showing significant motor responses in the intermediate layers of the SC. There were also differences between SUA and LFPs. LFPs showed a significant reversal of activity following the phasic visual response, suggesting that the neighboring neurons were suppressed. The results indicate that the LFP can be used as a reliable measure of the SC activity in lieu of SUA, and open up a new way to assess sensorimotor processing within the SC.

Automated Analysis Pipeline for Extracting Saccade, Pupil, and Blink Parameters Using Video-Based Eye Tracking.

The tremendous increase in the use of video-based eye tracking has made it possible to collect eye tracking data from thousands of participants. The traditional procedures for the manual detection and classification of saccades and for trial categorization (e.g., correct vs. incorrect) are not viable for the large datasets being collected. Additionally, video-based eye trackers allow for the analysis of pupil responses and blink behaviors. Here, we present a detailed description of our pipeline for collecting, storing, and cleaning data, as well as for organizing participant codes, which are fairly lab-specific but nonetheless, are important precursory steps in establishing standardized pipelines. More importantly, we also include descriptions of the automated detection and classification of saccades, blinks, "blincades" (blinks occurring during saccades), and boomerang saccades (two nearly simultaneous saccades in opposite directions where speed-based algorithms fail to split them), This is almost entirely task-agnostic and can be used on a wide variety of data. We additionally describe novel findings regarding post-saccadic oscillations and provide a method to achieve more accurate estimates for saccade end points. Lastly, we describe the automated behavior classification for the interleaved pro/anti-saccade task (IPAST), a task that probes voluntary and inhibitory control. This pipeline was evaluated using data collected from 592 human participants between 5 and 93 years of age, making it robust enough to handle large clinical patient datasets. In summary, this pipeline has been optimized to consistently handle large datasets obtained from diverse study cohorts (i.e., developmental, aging, clinical) and collected across multiple laboratory sites.

Saccades, pupil response and blink abnormalities in Huntington's disease patients during free viewing.

OBJECTIVE: Video-based eye tracking was used to investigate saccade, pupil, and blink abnormalities among patients with Huntington's disease (HD) who watched sequences of short videos. HD, an autosomal dominant neurodegenerative disorder resulting from a CAG mutation on chromosome 4, produces motor and cognitive impairments including slow or irregular eye movements, which have been studied using structured tasks. METHODS: To explore how HD affects eye movements under instruction free conditions, we assessed 22 HD patients and their age matched controls in a 10-minute video-based free viewing task. RESULTS: Patients with HD experienced a significant reduction in saccade exploration rate following video clip transitions, an increase in pupil reactions to luminance changes after clip transitions, and a significant higher blink rate throughout the task compared to the control group. CONCLUSIONS: These results show that HD has a significant impact on how patients visually explore and respond to their environment under unconstrained and ecologically natural conditions. SIGNIFICANCE: Eye tracking in HD patients revealed saccadic, pupil, and blink abnormalities in early HD patients, suggestive of brain circuitry abnormalities that probably involve brain stem deficits. Further research should explore the impact of these changes on the quality of life of the patients affected by the disease.

Attentional modulation of eye blinking is altered by sex, age, and task structure.

Spontaneous eye blinking is gaining popularity as a proxy for higher cognitive functions, as it is readily modulated by both environmental demands and internal processes. Prior studies were impoverished in sample size, sex representation and age distribution, making it difficult to establish a complete picture of the behavior. Here we present eye-tracking data from a large cohort of normative participants (n=604, 393 F, aged 5-93 years) performing two tasks: one with structured, discrete trials (interleaved pro/anti-saccade task; IPAST) and one with a less structured, continuous organization in which participants watch movies (free-viewing; FV). Sex- and age-based analyses revealed that females had higher blink rates between the ages of 22 and 58 years in the IPAST, and 22 and 34 years in FV. We derived a continuous measure of blink probability to reveal behavioral changes driven by stimulus appearance in both paradigms. In the IPAST, blinks were suppressed near stimulus appearance, particularly on correct anti-saccade trials, which we attribute to the stronger inhibitory control required for anti-saccades compared to pro-saccades. In FV, blink suppression occurred immediately after scene changes, and the effect was sustained on scenes where gaze clustered among participants (indicating engagement of attention). Females were more likely than males to blink during appearance of novel stimuli in both tasks, but only within the age bin of 18-44 years. The consistency of blink patterns in each paradigm endorses blinking as a sensitive index for changes in visual processing and attention, while sex and age differences drive interindividual variability.Significance Statement Eye-tracking is becoming useful as a non-invasive tool for detecting preclinical markers of neurological and psychiatric disease. Blinks are understudied despite being an important supplement to saccade and pupil eye-tracking metrics. The present study is a crucial step in developing a healthy baseline for blink behavior to compare to clinical groups. While many prior blink studies suffered from small sample sizes with relatively low age- and sex-diversity (review by Jongkees & Colzato, 2016), our large cohort of healthy participants has permitted a more detailed analysis of sex and age effects in blink behavior. Furthermore, our analysis techniques are robust to temporal changes in blink probability, greatly clarifying the relationship between blinking, visual processing, and inhibitory control mechanisms on visual tasks.

Microstimulation of the monkey superior colliculus induces pupil dilation without evoking saccades.

The orienting reflex is initiated by a salient stimulus and facilitates quick, appropriate action. It involves a rapid shift of the eyes, head, and attention and other physiological responses such as changes in heart rate and transient pupil dilation. The SC is a critical structure in the midbrain that selects incoming stimuli based on saliency and relevance to coordinate orienting behaviors, particularly gaze shifts, but its causal role in pupil dilation remains poorly understood in mammals. Here, we examined the role of the primate SC in the control of pupil dynamics. While requiring monkeys to keep their gaze fixed, we delivered weak electrical microstimulation to the SC, so that saccadic eye movements were not evoked. Pupil size increased transiently after microstimulation of the intermediate SC layers (SCi) and the size of evoked pupil dilation was larger on a dim versus bright background. In contrast, microstimulation of the superficial SC layers did not cause pupil dilation. Thus, the SCi is directly involved not only in shifts of gaze and attention, but also in pupil dilation as part of the orienting reflex, and the function of pupil dilation may be related to increasing visual sensitivity. The shared neural mechanisms suggest that pupil dilation may be associated with covert attention.

A retinotopic attentional trace after saccadic eye movements: evidence from event-related potentials.

Saccadic eye movements are a major source of disruption to visual stability, yet we experience little of this disruption. We can keep track of the same object across multiple saccades. It is generally assumed that visual stability is due to the process of remapping, in which retinotopically organized maps are updated to compensate for the retinal shifts caused by eye movements. Recent behavioral and ERP evidence suggests that visual attention is also remapped, but that it may still leave a residual retinotopic trace immediately after a saccade. The current study was designed to further examine electrophysiological evidence for such a retinotopic trace by recording ERPs elicited by stimuli that were presented immediately after a saccade (80 msec SOA). Participants were required to maintain attention at a specific location (and to memorize this location) while making a saccadic eye movement. Immediately after the saccade, a visual stimulus was briefly presented at either the attended location (the same spatiotopic location), a location that matched the attended location retinotopically (the same retinotopic location), or one of two control locations. ERP data revealed an enhanced P1 amplitude for the stimulus presented at the retinotopically matched location, but a significant attenuation for probes presented at the original attended location. These results are consistent with the hypothesis that visuospatial attention lingers in retinotopic coordinates immediately following gaze shifts.

Competitive integration of visual and goal-related signals on neuronal accumulation rate: a correlate of oculomotor capture in the superior colliculus.

The mechanisms that underlie the integration of visual and goal-related signals for the production of saccades remain poorly understood. Here, we examined how spatial proximity of competing stimuli shapes goal-directed responses in the superior colliculus (SC), a midbrain structure closely associated with the control of visual attention and eye movements. Monkeys were trained to perform an oculomotor-capture task [Theeuwes, J., Kramer, A. F., Hahn, S., Irwin, D. E., & Zelinsky, G. J. Influence of attentional capture on oculomotor control. Journal of Experimental Psychology. Human Perception and Performance, 25, 1595-1608, 1999], in which a target singleton was revealed via an isoluminant color change in all but one item. On a portion of the trials, an additional salient item abruptly appeared near or far from the target. We quantified how spatial proximity between the abrupt-onset and the target shaped the goal-directed response. We found that the appearance of an abrupt-onset near the target induced a transient decrease in goal-directed discharge of SC visuomotor neurons. Although this was indicative of spatial competition, it was immediately followed by a rebound in presaccadic activation, which facilitated the saccadic response (i.e., it induced shorter saccadic RT). A similar suppression also occurred at most nontarget locations even in the absence of the abrupt-onset. This is indicative of a mechanism that enabled monkeys to quickly discount stimuli that shared the common nontarget feature. These results reveal a pattern of excitation/inhibition across the SC visuomotor map that acted to facilitate optimal behavior-the short duration suppression minimized the probability of capture by salient distractors, whereas a subsequent boost in accumulation rate ensured a fast goal-directed response. Such nonlinear dynamics should be incorporated into future biologically plausible models of saccade behavior.

Separate visual signals for saccade initiation during target selection in the primate superior colliculus.

The primary function of the superior colliculus (SC) is to orient the visual system toward behaviorally relevant stimuli defined by features such as color. However, a longstanding view has held that visual activity in the SC arises exclusively from achromatic pathways. Recently, we reported evidence that the primate SC is highly sensitive to signals originating from chromatic pathways, but these signals are delayed relative to luminance signals (White et al., 2009). Here, we describe a functional consequence of this difference in visual arrival time on the processes leading to target selection and saccade initiation. Two rhesus monkeys performed a simple color-singleton selection task in which stimuli carried a chromatic component only (target and distractors were isoluminant with the background, but differed in chromaticity) or a combined chromatic-achromatic component (36% luminance contrast added equally to all stimuli). Although visual responses were delayed in the chromatic-only relative to the combined chromatic-achromatic condition, SC neurons discriminated the target from distractors at approximately the same time provided stimulus chromaticity was held constant. However, saccades were triggered sooner, and with more errors, with the chromatic-achromatic condition, suggesting that luminance signals associated with these stimuli increased the probability of triggering a saccade before the target color was adequately discriminated. These results suggest that separate mechanisms may independently influence the saccadic command in the SC, one linked to the arrival time of pertinent visual signals, and another linked to the output of the visual selection process.

Interaction between visual- and goal-related neuronal signals on the trajectories of saccadic eye movements.

During natural viewing, the trajectories of saccadic eye movements often deviate dramatically from a straight-line path between objects. In human studies, saccades have been shown to deviate toward or away from salient visual distractors depending on visual- and goal-related parameters, but the neurophysiological basis for this is not well understood. Some studies suggest that deviation toward is associated with competition between simultaneously active sites within the intermediate layers of the superior colliculus (SC), a midbrain structure that integrates sensory and goal-related signals for the production of saccades. In contrast, deviation away is hypothesized to reflect a higher-level process, whereby the neural site associated with the distractor isactively suppressed via a form of endogenous, top-down inhibition. We tested this hypothesis by measuring presaccadic distractor-evoked activation of SC visuomotor neurons while monkeys performed a simple task configured specifically to induce a high degree of saccades that deviate away. In the SC, cognitive processes such as top-down expectation are represented as variation in the sustained, low-frequency presaccadic discharge. We reasoned that any inhibition at the distractor-related locus associated with saccade deviation should affect the excitability of the neuron, thereby affecting the discharge rate. We found that, although the task produced robust deviation away, there was no evidence of a relationship between saccade deviation and distractor-evoked activation outside a short perisaccadic window that began no earlier than 22 msec before saccade onset. This indicates that deviation away is not adequately explained by a form of sustained, top-down inhibition at the distractor-related locus in the SC. The results are discussed in relation to the primary sources of inhibition associated with saccadic control.

Linking visual response properties in the superior colliculus to saccade behavior.

Here we examined the influence of the visual response in the superior colliculus (SC) (an oculomotor control structure integrating sensory, motor and cognitive signals) on the development of the motor command that drives saccadic eye movements in monkeys. We varied stimulus luminance to alter the timing and magnitude of visual responses in the SC and examined how these changes correlated with resulting saccade behavior. Increasing target luminance resulted in multiple modulations of the visual response, including increased magnitude and decreased response onset latency. These signal modulations correlated strongly with changes in saccade latency and metrics, indicating that these signal properties carry through to the neural computations that determine when, where and how fast the eyes will move. Thus, components of the earliest part of the visual response in the SC provide important building blocks for the neural basis of the sensory-motor transformation, highlighting a critical link between the properties of the visual response and saccade behavior.