Stimulus-dependent contrast sensitivity asymmetries around the visual field

Asymmetries in visual performance at isoeccentric locations are known as performance fields. At a fixed eccentricity, visual performance is best along the horizontal, intermediate along the lower vertical, and poorest along the upper vertical meridian. These performance fields are pervasive across a range of visual tasks, including those mediated by contrast sensitivity. However, contrast performance fields have not been characterized with a systematic manipulation of stimulus spatial frequency, eccentricity, and size; three parameters that constrain contrast sensitivity. Further, individual differences in performance fields measurements have not been assessed. Here, we use an orientation discrimination task to characterize the pattern of contrast sensitivity across four isoeccentric locations along the cardinal meridians, and to examine whether and how this asymmetry pattern changes with systematic manipulation of stimulus spatial frequency (4 cpd to 8 cpd), eccentricity (4.5° to 9°), and size (3° visual angle to 6° visual angle). Our data demonstrate that contrast sensitivity is highest along the horizontal, intermediate along the lower vertical, and poorest along the upper vertical meridian. This pattern is consistent across stimulus parameter manipulations, even though they cause profound shifts in contrast sensitivity. Eccentricity-dependent decreases in contrast sensitivity can be compensated for by scaling stimulus size alone. Moreover, we find that individual variability in the strength of performance field asymmetries is consistent across conditions. This study is the first to systematically and jointly manipulate, and compare, contrast performance fields across spatial frequency, eccentricity, and size, and to address individual variability in performance fields.

Impact of Stimulus Polarity on oVEMP Response Using the Belly-Tendon Electrode Montage

One stimulus parameter not well established with respect to the ocular vestibular evoked myogenic potential (oVEMP) is stimulus polarity. Many research studies traditionally record oVEMPs using alternating polarity primarily.The purpose of this study was to evaluate the effects of stimulus polarity on the oVEMP response under three different conditions (condensation, rarefaction, and alternating) with updated but established recording procedures—the belly-tendon electrode montage.oVEMPs were assessed with changes in stimulus polarity in the seated upright position.Thirty otologically normal participants (60 ears) with no history of hearing or balance disorders and normal middle ear function.Five hundred–hertz air-conducted tone bursts at 95-dB nHL were used to evoke the oVEMP response while recordings were made from the contralateral eye to acoustical stimulation using the belly-tendon electrode montage. Measurements were made using three polarities: alternating, condensation, and rarefaction. Natus Bio-logic AEP hardware and software was used for all data collection and analysis.Condensation stimulus phase provided the largest response amplitude compared with alternating and/or rarefaction. Rarefaction provided the earliest latency among stimulus polarities.Condensation is a more effective stimulus polarity regarding response amplitude when recording the oVEMP. This study further supports the use of the belly-tendon electrode montage for recording the oVEMP response.

THE INFLUENCED REGIONS OF ANESTHESIA ACUPUNCTURE AT SHENSHU OR JIAJI-L2 ACUPOINTS

Background: This research examined the influenced regions of Shenshu or Jiaji-L2 acupoints on human body after electronic anesthesia acupuncture and monitored side effect. Materials and Method: This is basic study, experimental analysis. To examined pain threshold at points of whole body’s dermatomes before and after anesthesia acupuncture on Shenshu or Jiaji-L2 acupoints. Thirty-two healthy volunteers were used electronic stimulus parameter with two phases symmetric thorn pulse, 160Hz, 20 minutes, cathode on the left acupoint and anode on the right acupoint. Data analyzed with SPSS16.0 software. Results: For Shenshu acupoints: Pain threshold were increased symmetrically from dermatome T6 to dermatome S1 on two sides of dorsal body, and diastolic blood pressure was increased significantly (p=0.003). For Jiaji-L2 acupoints: Pain threshold increased symmetrically from dermatome T11 to dermatome L4 on two sides of dorsal body. This study was safe and had no side effects. Conclusion: The influenced regions of Shenshu acupoints were from dermatome T6 to dermatome S1. The influenced regions of Jiaji-L2 acupoints were from dermatome T11 to dermatome L4. Keywords: Acupoint, Shenshu, Jiaji-L2, pain threshold, dermatome, anesthesia acupuncture