C++ function call missing argument list; use '&Runner::runTask' to create a pointer to member

This question seems to have been answered before on SO, but despite looking at other solutions I'm still not able to figure out why I am getting the error:

function call missing argument list; use '&Runner::runTask' to create a pointer to member

I have a class Runner which is going to be responsible for scheduling tasks to run any sub-work on separate threads asynchronously.

In the start method of my runner I have the following code:

void start(const bool runTaskAsync = true)
{
    if(!isRunning()) return;

    running = true;

    if(runTaskAsync)
    {
        Worker = std::thread(runTask, this);
    } 
    else 
    {
        this->runTask();
    }
}

The troublesome line that the compiler doesn't like is: Worker = std::thread(runTask, this);. Based on the error given (and the other questions asked on this site, I attempted to do the following)

Worker = std::thread(&Runner::runTask);

However I am still getting the same error. The runTask method is a private method on the Runner class and is defined as:

void runTask()
{
    while(isRunning())
    {
        // this_thread refers to the thread which created the timer
        std::this_thread::sleep_for(interval);
        if(isRunning())
        {
            // Function is a public method that we need to call, uses double parens because first calls the function called Function
            // and then the second set of parens calls the function that the calling Function returns
            Function()();
        }
    }
}

The call to Function()() calls the template function passed to the Runner instance, Runners private member variable of task is signed as std::function<void(void)> task; and the implementation of Function()() is signed as:

const std::function<void(void)> &Function() const 
{
    return task;
}

Which when called (as I understand) will run Function() and will then run task()

If there are any other details required please let me know. I am not currently instantiating any instance of Runner, I've simply included Runner.h in my main.cpp file to see whether it would compile.