Channel Configurations

These analog channel assignments are fundamental to the program's design and cannot be altered by the user, although most rigs do not use all of the dedicated signals described here. For example, the secondary eye locus (HGPOS2, VEPOS2) is rarely used, so channels AI<11> and AI<14> may be dedicated to some other task. And since Maestro 3.0 no longer supports the optics bench targets Fiber1 and Fiber2, analog channels AI<4,5> and AI<9,10> are available to record any other signals important to the investigation at hand. Digital inputs are used to timestamp the occurrences of TTL edge-triggered events, the most important of which are spikes recorded on an extracellular electrode (TTL pulses are generated by a window discriminator monitoring the output of the electrode preamplifier). Another typical usage is to timestamp the occurrence of marker pulses which are delivered at prescribed times during a trial or stimulus run -- e.g., to mark the point in time at which a stimulus is turned on or off. Finally, there are several "virtual" channels that represent the computed trajectories of fixation targets.For any given experiment, the investigator is only interested in a subset of these available data channels. To keep data file sizes to a minimum, only relevant analog channels are selected for recording. TTL events detected on any digital input channel are always recorded in the data file, while computed channel data is never recorded since it can be reconstructed offline. Thus, a record ON/off flag really only applies to the analog input channels. In addition, up to 10 channels can be flagged for display in the Data Traces panel during an experiment. Other attributes set the channel trace gain, offset, and color to make it easier to interpret the display of multiple traces. The Maestro channel configuration object defines the complete set of these attributes for all available data channels, as well as the y-axis range for the data trace display. Since the set of relevant data channels may be different for different kinds of experiments, Maestro allows the user to define multiple channel configurations, all of which are grouped together under the Channels branch of the document object tree.

Editing a channel configuration in the Channels Editor

To create a channel configuration, make sure the keyboard focus is on the document object tree, select the appropriate item from the Object|New menu, give it a name, and double-click on the label in the object tree to load the channels definition into the Channels Editor, which is the fourth panel in the tabbed window on the right side of the Maestro frame window's client area. Most of the editor panel is taken up by yet another grid control, which displays several attributes for each of the data channels, as described in the preceding section. The grid is rather long, so you will likely need to scroll down to see all of it.

• • Record? -- This flag determines whether or not the data channel is recorded during the experiment (ON) or not (off). It applies only to the analog input channels -- events on the digital inputs are always saved in Maestro data files, and computed channels are never recorded. Note that the corresponding cells are disabled (background is gray) for the digital and computed channels. To toggle the flag's state, simply right-click on the cell.

  • Display? -- This flag determines whether or not the channel's data trace appears in the Data Traces display window. Again, use a right-click to toggle the flag's state. However, Maestro will not let you display more than 10 channels at one time. Once you have toggled ON the Display? flag for 10 channels, you will not be able to turn on any more of them.

  • Offset -- If you are displaying more than a couple traces in the Data Traces window, the resulting display may be confusing if all traces have the same baseline. This parameter specifies a baseline offset in millivolts. Use it to redistribute multiple traces along the vertical extent of the trace display. There are two ways to edit the parameter. A right-click on the cell will increase the value by 500mV, while a Shift-right-click will decrement it by 500mV. Alternatively, double-click on the cell to invoke the usual in-place edit control and type in the desired offset. Any integer in [-90000 ... 90000] is admissible.

  • Multiplier -- Use this attribute to scale a displayed data trace by an integral power of 2. The attribute value is the exponent N for the scale factor 2^N; any integer in [-5..5] is allowed. Note that the scale factor only affects the displayed data; the recorded data streams are not scaled. Use a right-click or Shift-right-click to increment or decrement the attribute value, respectively; or, double-click on the cell to invoke an in-place combo box and choose a new value from the combo box dropdown list. Note that this parameter does not apply to the digital input channels (the corresponding cells are grayed out). The data trace for a digital channel is simply a pulse train raster; there's no need to scale the trace.

  • Trace Color -- Sets the color of the channel's display trace in the Data Traces window. You can choose from any of 12 different colors: white, red, green, blue, yellow, magenta, cyan, dark green, orange, purple, pink, and medium gray. The cell's background reflects the color chosen. To change the color, right-click on the cell repeatedly until you find the desired color. Alternatively, double-click on the cell to invoke an in-place combo box and choose a color from its dropdown list.

In addition to the channels grid, there are three pushbuttons and two edit controls on the left side of the Channels Editor. The edit controls set the Y-axis range of the Data Traces display, in millivolts. The endpoints of the range must be integers in [-99999 .. 99999]. Adjust the Y-axis range and the individual channel Offset attributes to provide adequate spacing between the channel traces. The pushbuttons execute wholesale changes on the channels grid. Pressing the Restore Defaults pushbutton will reset the channel grid to a default state (try it!). The Common Axis command zeroes the Offset and Multiplier attributes for all channels in the table, sets trace colors to white, then assigns a different color to each channel that is enabled for display in the Data Traces window. Finally, the Space Evenly command performs the same changes as the Common Axis command, then sets the Offset attributes of any displayed traces to evenly distribute their baselines along the current Y-axis range. All digital channels are assigned the same baseline offset, near the top of the Y-axis range.