Aerial visual acuity in harbor seals (<Emphasis Type="Italic">Phoca vitulina</Emphasis>) as a function of luminance

In this study, we measured aerial visual acuity in harbor seals. As a first approach to the hypothesis that harbor seals can obtain acute aerial visual acuity mediated by the interaction of the vertical slit-shaped pupil and the corneal flattening although refractive measurements had revealed aerial myopia, visual acuity was tested as a function of luminance and pupil dilation. We analyzed aerial visual acuity (minimal resolvable stripe width) in three harbor seals in a two-alternative-forced-choice discrimination experiment. Our results further support the hypothesis that harbor seals possess an aerial visual acuity comparable to the acuity in clear waters if the vertical slit pupil does not exceed the zone of corneal flattening in bright light. When the pupil dilates with decreasing luminance, visual acuity decreases which might be due to deflected light from the stronger curved peripheral cornea.     

用显示器测量办公亮度环境下的人眼对比度敏感视觉特性

对比度敏感是描述人眼视觉系统空间特性的主要指标之一,对比度敏感函数是反映不同条件下的对比度敏感与空间频率之间的关系。人眼对比度敏感数据的测量受到环境亮度较大的影响,为了研究常用办公环境条件下的人眼对比度敏感情况,对6位青年在环境亮度分别为153,312,470 cd/m2和暗室条件下,在距离为2米处观测11种空间频率的矩形光栅进行测量,光栅用显示器进行显示,其平均亮度分别为60和90 cd/m2。实验结果表明,对于相同频率的光栅,人眼对比度敏感程度随着环境亮度的增加而减小,而且人眼在暗室环境下比在办公环境条件下对亮度光栅更敏感;但是在观测平均亮度为60cd/m2的光栅时,人眼特殊地对在环境亮度为312 cd/m2的条件下更敏感。     

用显示器测量办公亮度环境下的人眼对比度敏感视觉特性

对比度敏感是描述人眼视觉系统空间特性的主要指标之一,对比度敏感函数是反映不同条件下的对比度敏感与空间频率之间的关系。人眼对比度敏感数据的测量受到环境亮度较大的影响,为了研究常用办公环境条件下的人眼对比度敏感情况,对6位青年在环境亮度分别为153,312,470 cd/m2和暗室条件下,在距离为2米处观测11种空间频率的矩形光栅进行测量,光栅用显示器进行显示,其平均亮度分别为60和90 cd/m2。实验结果表明,对于相同频率的光栅,人眼对比度敏感程度随着环境亮度的增加而减小,而且人眼在暗室环境下比在办公环境条件下对亮度光栅更敏感;但是在观测平均亮度为60cd/m2的光栅时,人眼特殊地对在环境亮度为312 cd/m2的条件下更敏感。     

Shape discrimination by wasps (<Emphasis Type="Italic">Paravespula germanica</Emphasis>) at the food source: generalization among various types of contrast

Wasps (Paravespula germanica) were trained and tested at an artificial feeding site, using convex shapes that produced colour contrast, luminance contrast, or motion contrast against the background. With each of the three types of contrast, we tested the wasps capacity to discriminate the learned shape from novel shapes. In addition, in each experiment we tested the wasps capability to recognize the learned shape when it offered a different type of contrast than that it had during the training. With the coloured shapes, a side-glance at the colour discrimination performance of the wasps was possible in addition. Wasps are found to discriminate between a variety of convex shapes regardless of the type of contrast that they produce against the background. Mainly, they discriminate the learned shape from novel shapes even if the colour of the shapes or the type of contrast they produce against the background is altered in the test. Thus, wasps generalize the learned shape from one colour to another, as well as between colour contrast, luminance contrast, and motion contrast.     

Enabling High Grayscale Resolution Displays and Accurate Response Time Measurements on Conventional Computers

Display systems based on conventional computer graphics cards are capable of generating images with 8-bit gray level resolution. However, most experiments in vision research require displays with more than 12 bits of luminance resolution. Several solutions are available. Bit++ ¹ and DataPixx ² use the Digital Visual Interface (DVI) output from graphics cards and high resolution (14 or 16-bit) digital-to-analog converters to drive analog display devices. The VideoSwitcher ³ described here combines analog video signals from the red and blue channels of graphics cards with different weights using a passive resister network ⁴ and an active circuit to deliver identical video signals to the three channels of color monitors. The method provides an inexpensive way to enable high-resolution monochromatic displays using conventional graphics cards and analog monitors. It can also provide trigger signals that can be used to mark stimulus onsets, making it easy to synchronize visual displays with physiological recordings or response time measurements.Although computer keyboards and mice are frequently used in measuring response times (RT), the accuracy of these measurements is quite low. The RTbox is a specialized hardware and software solution for accurate RT measurements. Connected to the host computer through a USB connection, the driver of the RTbox is compatible with all conventional operating systems. It uses a microprocessor and high-resolution clock to record the identities and timing of button events, which are buffered until the host computer retrieves them. The recorded button events are not affected by potential timing uncertainties or biases associated with data transmission and processing in the host computer. The asynchronous storage greatly simplifies the design of user programs. Several methods are available to synchronize the clocks of the RTbox and the host computer. The RTbox can also receive external triggers and be used to measure RT with respect to external events. Both VideoSwitcher and RTbox are available for users to purchase. The relevant information and many demonstration programs can be found at http://lobes.usc.edu/.