This function evaluates a hemodynamic response function (HRF) object for a given set of time points (grid) and other parameters. It handles both point evaluation (duration=0) and block evaluation (duration > 0).
Usage
# S3 method for class 'HRF'
evaluate(
x,
grid,
amplitude = 1,
duration = 0,
precision = 0.2,
summate = TRUE,
normalize = FALSE,
...
)Arguments
- x
The HRF object (inherits from `HRF` and `function`).
- grid
A numeric vector of time points at which to evaluate the HRF.
- amplitude
The scaling value for the event (default: 1).
- duration
The duration of the event (seconds). A duration of 0 is an impulse of unit mass and returns the HRF itself; a duration > 0 is a unit-height boxcar and returns its integral against the HRF (default: 0).
- precision
The quadrature step used to integrate over the block when duration > 0 (default: 0.2). It controls numerical accuracy only: the result converges as `precision` decreases and does not otherwise depend on it.
- summate
Logical; if TRUE (default), integrate the HRF over a unit-height block. If FALSE, divide by the duration to obtain a temporal average. The peak still varies with duration and can decrease for longer blocks. The average approaches the impulse response as duration approaches zero. Use `normalize = TRUE` for unit-peak scaling on the evaluated grid.
- normalize
Logical; scale output so that the peak absolute value is 1 (default: FALSE). Applied *after* amplitude scaling and duration processing.
- ...
Additional arguments (unused).
Examples
# Evaluate canonical HRF at specific times
times <- seq(0, 20, by = 0.5)
response <- evaluate(HRF_SPMG1, times)
# Evaluate with amplitude scaling
response_scaled <- evaluate(HRF_SPMG1, times, amplitude = 2)
# Evaluate with duration (block design)
response_block <- evaluate(HRF_SPMG1, times, duration = 5, summate = TRUE)
# Multi-basis HRF evaluation
response_multi <- evaluate(HRF_SPMG3, times) # Returns 3-column matrix