Heading angle

The question

Right, let's get our feet wet. If we only watch the first seconds of a swim, what can the animal's direction tell us? You're watching Morris Water Maze Software Guide, over at morriswatermazesoftware.com.

Meet the heading angle

Heading angle, or initial heading error, is the angle between the way the animal sets off and the straight line to the platform. A small angle means it knew which way to go from the start, which is a strong sign of a place memory that works from more than one start point. Related tests, such as a corridor or a cone towards the goal, ask the same question in a slightly different way: did the first part of the path head for the target?

How it runs

So, what does a session look like? First, pick a clear start window, such as the heading after the animal has left the wall, or in the first second or two of the trial. Next, draw the ideal line from that point to the platform, or to its old spot in a probe. Then, measure the angle between the animal's heading and that line. Finally, average the absolute angle across start points, so left and right errors do not cancel.

Strengths and limits

Why do labs keep coming back to it? It captures knowledge of direction before the animal can bump into the platform by chance. It works from every start point, which is the point of a place memory. It is easy to compare across days and groups. And the catch? Early wall-hugging or a delayed start can make the first heading look worse than the later search. The start window must be fixed, or the numbers will shift.

What to measure

This is where tracking software earns its keep. Initial heading error: the absolute angle off the direct line at the start. Percentage of trials within a small angle: a simple accuracy rate, often within 20 or 30 degrees of the goal. Corridor or cone test: whether the early path stayed inside a path aimed at the goal. Heading by start point: to check that the animal can aim from more than one place. A rat's latency is already short by day three, but its first heading is still 50 degrees off. It is finding the platform late in the swim, not aiming for it. By day five the heading error has dropped, and the path starts straight.

The takeaway

One thing to take away: percentage of trials within a small angle and its neighbours tell you how the task was done, not just how fast. Scripts, chapters and sources live on this page.