Psychtoolbox 3

Stimuli consisted of colored pictures of three male faces with neutral expressions, obtained from the NimStim database (Tottenham et al., 2009 (link)), along with 36 colored pictures of meat dishes and 36 colored pictures of vegetable dishes obtained from the Internet. Stimuli were presented with using Psychtoolbox 3.0.8 (Brainard, 1997 (link); Pelli, 1997 (link)) in MATLAB 7.8 (The MathWorks, Inc., Natick, MA, USA).
The stimuli were presented using an event-related design. In each trial, one of the three faces was presented along with a text cue above the face indicating the person’s emotional state (“happy” or “sad”), and pictures of a meat dish and a vegetable dish on the left and right of the face (Figure 1). Each trial was presented for 2 s and trials were separated by a 4–10 s jittered fixation interval. Each run consisted of six trials per condition (i.e., each face paired with each emotion) to give a total of 36 trials per run, and a run duration of 5 min. The program “optseq2”¹ was used to generate the optimal sequence and separation of trials for maximal statistical efficiency of rapid-presentation event-related hemodynamic response estimation for each run (Dale, 1999 (link)). The position of the meat and vegetable dishes on the left and right of the face was counterbalanced across trials within each condition and each run. Ten runs were presented.

Audiovisual signals were presented using Psychtoolbox 3.09 (www.psychtoolbox.org; Brainard, 1997 (link); Kleiner et al., 2007 ) running under Matlab R2010a (MathWorks). Auditory stimuli were presented at ∼75 dB SPL using MR-compatible headphones (MR Confon). Visual stimuli were back-projected onto a Plexiglas screen using an LCoS projector (JVC DLA-SX21). Participants viewed the screen through an extra-wide mirror mounted on the MR head coil, resulting in a horizontal visual field of ∼76° at a viewing distance of 26 cm. Participants indicated their response using an MR-compatible custom-built button device. Participants’ eye movements and fixation were monitored by recording participants’ pupil location using an MR-compatible custom-built infrared camera (sampling rate 50 Hz) mounted in front of the participants’ right eye and iView software 2.2.4 (SensoMotoric Instruments).

Audiovisual stimuli were presented using Psychtoolbox 3.09 (www.psychtoolbox.org) [38 (link)] running under MATLAB R2010a (MathWorks). Auditory stimuli were presented at ~75 dB SPL using MR-compatible headphones (MR Confon). Visual stimuli were back-projected onto a Plexiglas screen using an LCoS projector (JVC DLA-SX21). Participants viewed the screen through an extra-wide mirror mounted on the MR head-coil resulting in a horizontal visual field of approximately 76° at a viewing distance of 26 cm. Participants performed the localization task using an MR-compatible custom-built button device. Participants’ eye movements and fixation were monitored by recording participants’ pupil location using an MR-compatible custom-build infrared camera (sampling rate 50 Hz) mounted in front of the participants’ right eye and iView software 2.2.4 (SensoMotoric Instruments).

The three tasks were programmed using Matlab R2011a, Psychtoolbox 3.0 (MathWorks, Natick, USA), and each participant completed all trials. All stimuli were matrices consisting of 4 × 4 squares (Suchan et al., 2006 (link)), with each matrix containing 4 black squares and 12 white squares (see Fig. 1). The position of the 4 black squares within the matrix was altered for each different stimulus. Stimuli were presented in the center of a 17-inch NESO computer monitor with a vertical visual angle of 2.8°. The order for each task was counterbalanced across all participants.

Optogenetic stimulation was done with a 473 nm (blue) laser or with a 470 nm (blue) LED (Omicron Laserage). A 594 nm (yellow) laser was used as control. Laser light was delivered to cortex through a 100 μm or a 200 μm diameter multimode fiber (Thorlabs), LED light through a 2 mm diameter polymer optical fiber (Omicron Laserage). Fiber endings were placed just above the cortical surface, immediately next to the recording sites with a slight angle relative to the electrodes. Laser waveform generation used custom circuits in TDT, and timing control used Psychtoolbox-3, a toolbox in MATLAB (MathWorks) (Brainard, 1997 (link)).
For white noise stimulation, the laser was driven by normally distributed white noise, with light intensities updated at a frequency of 1017.1 Hz. For each recording session, the mean of the normal distribution was chosen to fall into the lower half of the dynamic range of the laser-response curve of the recorded MUA. This resulted in mean values in the range of 3-12 mW/mm² (13 MUA recording sites in the 3 cats showing expression of ChR2 in area 17). The standard deviation (SD) of the normal distribution was scaled to be 1/2 the mean. The resulting distributions were truncated at 3.5 SDs. The resulting range of laser intensities always excluded both zero and maximal available laser intensities and thereby avoided clipping.