, 2011). It is highly likely that this signal is modulated along the scanpath or has an attentional function thus providing the ground for context-dependent neuronal processing.
All experiments followed the National Institutes of Health Guide for the Care and Use of Laboratory Animals and ICG-001 datasheet were in accordance with University of Chile guidelines. All surgical and recording procedures are described in Maldonado et al. (2008). Three adult, male capuchin monkeys (Cebus apella) weighing 3–4 kg served as subjects for this study. Henceforth, these animals are referred to as monkeys D, M, and S. Under sterile conditions, each animal was implanted with a scleral search coil for monitoring eye position (2 kHz sampling rate, DNI Instruments, Resolution: 1.2 min of arc; for details see Judge et al., 1980), and a cranial post for head fixation. During the experiment, the animals were seated in a chamber dimly lit at a low scotopic level (1–2 lx, LX-110 Lux Meter). They were presented with a collection of 11 (monkeys D and S) and 4 (monkey M) pictures of different natural scenes (consisted of pictures of animals, faces and landscapes, 800 × 600 pixel resolution; taken from Corel® photo library). The pictures were displayed on a CRT computer monitor (frame rate: 60 Hz) located
Epacadostat 57 cm in front of the animals, subtending 40° × 30° of visual angle. As a control, for every third stimulus presentation, a blank frame with black background was presented instead of a natural image. We refer to the trials with natural image stimuli as image
condition trials and those with Histone demethylase the blank frame as blank condition trials. In order to maintain the alertness of the animals, and to control eye coil precision, they were trained to perform a fixation task before every trial, in which a black frame with a single fixation spot was presented and they had to fixate it (1° window) for 1 s in order to be rewarded (referred to as fixation cue). Then, a natural image or the blank frame was presented for 3 or 5 s for monkey D or S and M, respectively (free viewing trials) ( Fig. 1). In the free viewing trial, the animals were allowed to freely explore the monitor screen with self-initiated eye movements while the experimental protocol required the animals to maintain their gaze within the limits of the monitor for the whole presentation period, to be rewarded with a drop of juice. A session was composed of image condition trials and blank condition trials alternating with fixation cues. Before each session we calibrated the coil with a series of fixation cues, referred to as fixation epoch. If the monkeys were willing to continue to work after a session we ran a further session starting with a fixation epoch, followed by a new set of images. This process was repeated as long as the animals were motivated to continue the task. Only the data collected during the presentation of fixation cues and natural images served for the following analyses and defined an experimental session.