Related Experiment Video
Updated: Jul 5, 2026
11:38
In vivo Imaging of Optic Nerve Fiber Integrity by Contrast-Enhanced MRI in Mice
Published on: July 22, 2014
Contrast sensitivity loss with aging: sampling efficiency and equivalent noise at different spatial frequencies.
1Department of Optometry, Anglia Polytechnic University, East Road, Cambridge CB1 1PT, UK. s.pardhan@apu.ac.uk
Summary
Aging impairs vision through both optical and neural changes. Older adults showed reduced neural sampling efficiency and increased optical noise, varying by spatial frequency, indicating distinct age-related visual mechanisms.
Area of Science:
- Vision science
- Ophthalmology
- Neuroscience
Background:
- Visual function declines with age, attributed to both optical and neural factors.
- Understanding the distinct contributions of these factors is crucial for addressing age-related vision loss.
Purpose of the Study:
- To investigate the relative contributions of optical and neural factors to age-related visual decline.
- To measure contrast detection in young and older individuals across different spatial frequencies and noise levels.
Main Methods:
- Contrast detection thresholds were measured in young and older visually normal observers.
- Externally added visual noise was used to isolate optical (equivalent noise) and neural (sampling efficiency) contributions.
- Measurements were taken at three spatial frequencies: 1, 4, and 10 cycles per degree (c/deg).
Main Results:
- Older subjects exhibited significantly lower sampling efficiency at 1 and 4 c/deg, indicating neural changes.
- Older subjects demonstrated significantly higher equivalent noise levels at 10 c/deg, suggesting optical effects.
- The impact of neural and optical factors on contrast sensitivity loss varied with spatial frequency.
Conclusions:
- Both neural and optical factors contribute to age-related vision impairment.
- The specific mechanisms and their relative importance differ depending on the spatial frequency.
- This suggests distinct underlying physiological changes contributing to vision loss in aging individuals.
Related Concept Videos
01:01Perception of Sound Waves
The human ear is not equally sensitive to all frequencies in the audible range. It may perceive sound waves with the same pressure but different frequencies as having different loudness. Moreover, the perception of sound waves depends on the health of an individual's ears, which decays with age. The health of one's ears may also be affected by regular exposure to loud noises.
The pitch of a sound depends on the frequency and the pressure amplitude of the source. Two sounds of the same frequency...
The pitch of a sound depends on the frequency and the pressure amplitude of the source. Two sounds of the same frequency...
01:05Difference from Background: Limit of Detection
The limit of detection (LOD) is the smallest amount of analyte that can be distinguished from the background noise. The LOD value corresponds to the concentration at which the analyte signal is three times larger than the standard deviation of the blank signal. Below this value, the analyte signal cannot be differentiated from the background noise. It is calculated by dividing the calibration slope by 3 times the standard deviation of the blank signals.
The LOD indicates the presence or absence...
The LOD indicates the presence or absence...
01:15Sampling Theorem
In signal processing, the analysis of continuous-time signals, denoted as x(t), often involves sampling techniques to convert these signals into discrete-time signals. This process is essential for digital representation and manipulation. A critical component in sampling is the train of impulses, characterized by the sampling interval and the sampling frequency. The relationship between these parameters and the original signal's properties dictates the success of the sampling process.
01:18Aliasing
Accurate signal sampling and reconstruction are crucial in various signal-processing applications. A time-domain signal's spectrum can be revealed using its Fourier transform. When this signal is sampled at a specific frequency, it results in multiple scaled replicas of the original spectrum in the frequency domain. The spacing of these replicas is determined by the sampling frequency.
If the sampling frequency is below the Nyquist rate, these replicas overlap, preventing the original signal...
If the sampling frequency is below the Nyquist rate, these replicas overlap, preventing the original signal...
01:22Upsampling
Managing signal sampling rates is essential in digital signal processing to maintain signal integrity. A decimated signal, characterized by a reduced frequency range due to its lower sampling rate, can be upsampled by inserting zeros between each sample. This upsampling process expands the original spectrum and introduces repeated spectral replicas at intervals dictated by the new Nyquist frequency. To refine this zero-inserted sequence, it is passed through a lowpass filter with a cutoff...
01:27Pharmacodynamics in Geriatric Patients: Effects of Age
Age-related pharmacokinetic changes are extensively documented, but understanding age-related pharmacodynamic alterations is relatively limited. This knowledge gap can be partly attributed to the complexity of developing appropriate measures of drug responses compared to bioanalytical methods for determining drug concentrations.Most information regarding age-related differences in human pharmacodynamics originates from cross-sectional studies. However, these studies assume that observed mean...