xtos_signal_p300_feature

Computes a centered positive peak, z score, energy, and relative latency from a prestimulus baseline and millisecond window.

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Declaration

#include <xtos/signal.h>

int xtos_signal_p300_feature(const double *input,
                             size_t n,
                             uint32_t sample_rate_hz,
                             size_t baseline_samples,
                             uint32_t window_start_ms,
                             uint32_t window_end_ms,
                             double detection_z_threshold,
                             struct xtos_p300_feature *result);

Parameters

Parameter	Type	Description
input	const double *	Non-NULL array with at least n entries; the function does not modify it.
n	size_t	Sample count; it need not be a power of two.
sample_rate_hz	uint32_t	Sampling rate in Hz, greater than zero.
baseline_samples	size_t	Prestimulus baseline length, with 2≤baseline_samples<n.
window_start_ms	uint32_t	Window start after stimulus onset in milliseconds, less than the end value.
window_end_ms	uint32_t	Window end after stimulus onset in milliseconds; the end point is exclusive.
detection_z_threshold	double	Finite positive detection threshold.
result	struct xtos_p300_feature *	Non-NULL caller-provided output structure.

Output fields

Field	Type	Meaning
baseline_mean	double	Mean of baseline samples, in the same unit as input.
baseline_stddev	double	Population standard deviation of the baseline, in the same unit as input.
peak_amplitude	double	Maximum positive baseline-centered amplitude in the window, in the same unit as input.
peak_latency_ms	double	Peak latency relative to stimulus onset, in milliseconds.
peak_z_score	double	Z score peak_amplitude / baseline_stddev.
window_energy	double	Sum of squared centered samples in the window, in squared input units.
peak_index	size_t	Absolute input index of the peak sample.
detected	int	Whether peak_z_score reaches detection_z_threshold; 1 when reached, otherwise 0.

Return value

Returns 0 and writes result on success; returns -1 on failure. detected only means peak_z_score reached the threshold.

Errors

errno	Condition
EINVAL	Parameters or rounded window are invalid, or a checked baseline/window sample is NaN/Inf.
EDOM	The baseline standard deviation is zero or non-finite.

Notes

Milliseconds convert with (ms×fs+500)/1000; the peak is the greatest positive centered value in the window, keeping the earliest tie.
The implementation checks finite values in the baseline and window; samples outside those ranges are not checked.
The caller owns result and no heap is allocated; this is a research feature, not a diagnostic or calibration conclusion.

Example

Source

This reference describes headers and implementation at OpenXTOS commit dd313955ad57542bcd2af8827157d1bbd0cf5e83.