The output of the receivers is usually an open-collector output, which means that it requires a pull-up resistor to work. This output is normally switched off, so is pulled high by the pull-up resistor. When it receives a suitable IR modulated signal the output is turned on, pulling the output low. So 'on' is low, and 'off' is high, which is the opposite way to normal convention.
There are some details on IR communication in my PIC tutorials at - they are based on the Sony SIRC remote system.