What is a sonar pulse and how can it injure humans under water?

An echo sounder on a boat uses sound waves to help gauge the depth of the water. mark_vyz/Shutterstock Christine Erbe, Curtin University

Over the weekend, the Australian government revealed that last Tuesday its navy divers had sustained “minor injuries”, likely due to sonar pulses from a Chinese navy vessel.

The divers had been clearing fishing nets from the propellers of HMAS Toowoomba while in international waters off the coast of Japan. According to a statement from deputy prime minister Richard Marles, despite HMAS Toowoomba communicating with internationally recognised signals, the Chinese vessel approached the Australian ship and turned on its sonar, forcing the Australian divers to exit the water.

The incident prompted a response from the Australian government, who labelled the incident “unsafe and unprofessional”. But what exactly is a sonar pulse, and what kinds of injuries can sonar cause to divers?

What is sonar?

Light doesn’t travel well under water – even in clear waters, you can see perhaps some tens of metres. Sound, however, travels very well and far under water. This is because water is much denser than air, and so can respond faster and better to acoustic pressure waves – sound waves.

Because of these properties, ships use sonar to navigate through the ocean and to “see” under water. The word “sonar” stands for sound navigation and ranging.

Sonar equipment sends out short acoustic (sound) pulses or pings, and then analyses the echoes. Depending on the timing, amplitude, phase and direction of the echoes the equipment receives, you can tell what’s under water – the seafloor, canyon walls, coral, fishes, and of course ships and submarines.

Most vessels – from small, private boats to large commercial tankers – use sonar. However, compared to your off-the-shelf sonar used for finding fish, navy sonars are stronger.

What are the effects of sonar on divers?

This is a difficult topic to study, because you don’t want to deliberately expose humans to harmful levels of sound. There are, however, anecdotes from various navies and accidental exposures. There have also been studies on what humans can hear under water, with or without neoprene suits, hoods, or helmets.

We don’t hear well under water – no surprise, since we’ve evolved to live on land. Having said that, you would hear a sonar sound under water (a mid-to-high pitch noise) and would know you’ve been exposed.

When it comes to naval sonars, human divers have rated the sound as “unpleasant to severe” at levels of roughly 150dB re 1 µPa (decibel relative to a reference pressure of one micropascal, the standard reference for underwater sound). This would be perhaps, very roughly, 10km away from a military sonar. Note that we can’t compare sound exposure under water to what we’d receive through the air, because there are too many physical differences between the two.

Human tolerance limits are roughly 180dB re 1 µPa, which would be around 500m from military sonar. At such levels, humans might experience dizziness, disorientation, temporary memory and concentration impacts, or temporary hearing loss. We don’t have information on what levels the Australian divers were exposed to, but their injuries were described as minor.

At higher received levels, closer ranges, or longer exposures, you might see more severe physiological or health impacts. In extreme cases, in particular for impulsive, sudden sound (which sonar is not), sound can cause damage to tissues and organs.

What does sonar do to marine animals?

Some of the information on what noise might do to humans under water comes from studies and observations of animals.

While they typically don’t have outer ears (except for sea lions), marine mammals have inner ears that function similarly to ours. They can receive hearing damage from noise, just like we do. This might be temporary, like the ringing ears or reduced sensitivity you might experience after a loud concert, or it can be permanent.

Marine mammals living in a dark ocean rely on sound and hearing to a greater extent than your average human. They use sound to navigate, hunt, communicate with each other and to find mates. Toothed whales and dolphins have evolved a biological echo sounder or biosonar, which sends out series of clicks and listens for echoes. So, interfering with their sounds or impacting their hearing can disrupt critical behaviours.

Finally, sound may also impact non-mammalian fauna, such as fishes, which rely on acoustics rather than vision for many of their life functions.

Christine Erbe, Director, Centre for Marine Science & Technology, Curtin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Read More........→November 22, 2023

Polar bears may struggle to produce milk for their cubs as climate change melts sea ice

During their time onshore, polar bear mothers may risk their survival by continuing to nurse when food is not available. (Shutterstock) Louise Archer, University of Toronto

When sea ice melts, polar bears must move onto land for several months without access to food. This fasting period is challenging for all bears, but particularly for polar bear mothers who are nursing cubs.

Our research, published in Marine Ecology Progress Series, found that polar bear lactation is negatively affected by increased time spent on land when sea ice melts.

Impaired lactation has likely played a role in the recent decline of several polar bear populations. This research also indicates how polar bear families might be impacted in the future by continued sea-ice loss caused by climate warming.

Challenges of rearing cubs

While sea ice might appear as a vast and perhaps vacant ecosystem, the frozen Arctic waters provide an essential platform for polar bears to hunt energy-rich seals — the bread and butter of their diet.

Sea ice is a dynamic environment that can vary through time and in different regions of the Arctic. Polar bears in Canada’s western Hudson Bay area experience seasonal sea ice, which melts in the warmer summer months, forcing the polar bears to move onto land until cooler winter temperatures cause the sea ice to refreeze.

On shore, polar bears often remain in a fasting state, using their body stores of fat for fuel. (Shutterstock)

While on shore, hunting opportunities are rare and polar bears generally spend their time in a fasting state. Polar bears rely on their immense body fat stores to fuel them during these leaner months, with some individuals measuring almost 50 per cent body fat when they come onshore in early summer.

While on land, polar bears can lose around a kilogram of body mass per day, so making it to the end of the ice-free season requires them to carefully manage their energy. For most polar bears, this means reducing activity levels and conserving energy until the sea ice returns and seal hunting can resume.

Females with cubs must also factor in the additional burden of lactation. Polar bears produce high-energy milk, which — at up to 35 per cent fat — is like whipping cream. This high-fat milk allows cubs to grow quickly, increasing from just 600 grams at birth to well over 100 kilograms by the time they are around two-and-a-half years old and leave their mothers to become independent.

During the onshore fasting period, polar bear mothers face a difficult trade-off: Stop lactating and risk the health of her growing cubs or continue nursing and risk her own survival as her energy reserves are depleted.

Polar bear cubs remain with their mothers for up to two-and-a-half years. (Shutterstock)

Moderating lactation

Although lactation is important to both mothers and cubs, studies on polar bear lactation are relatively rare.

To better understand how females manage their lactation investment, our research team revisited a data set of polar bear milk samples collected in the late 1980s and early 1990s from polar bears on land during the ice-free period.

We estimated how long each polar bear mom had been fasting based on annual sea-ice breakup dates and found that the energy content of their milk declined the more days spent onshore. Some bears had stopped producing milk entirely. Both milk energy content and lactation probability were negatively related to the mother’s body condition, meaning females in poor body condition had to prioritize their own energetic needs over their cubs.

The bears who reduced their investment in lactation benefited by using up less of their body reserves, meaning they could fast for longer. Yet the cubs who received lower energy milk grew more slowly than offspring of females that maintained their lactation effort. In the long term, this may reduce cub survival and, ultimately, negatively affect population dynamics.

Climate change and population declines

After around three months on land, the probability of a female with cubs lactating was 53 per cent. This dropped to 35 per cent for a female with yearlings (older cubs from the previous year).

The data in our study were collected around three decades ago. Since then, climate warming has meant that the ice-free season in western Hudson Bay has been extending by around seven days per decade. Polar bears are now regularly forced to spend more than four months on land.

As the ice-free season has increased and polar bears must go for longer without food, their average body condition has declined. The ability of female polar bears to nurse their cubs has probably also become increasingly impaired.

This may have contributed to the 50 per cent decline in the population size of the western Hudson Bay population over the last four decades, and is likely to contribute to further declines if climate warming and sea-ice declines continue as projected without mitigation.

This research adds another piece to our understanding of polar bear resilience to climate change. Without action to halt climate warming and sea-ice loss, survival of cubs will be at risk across the Arctic.

Louise Archer, Postdoctoral Fellow, Biological Sciences, University of Toronto

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Read More........→October 09, 2023

Is it normal to forget words while speaking? And when can it spell a problem?

mimi thian/unsplash Greig de Zubicaray, Queensland University of TechnologyWe’ve all experienced that moment mid-sentence when we just can’t find the word we want to use, even though we’re certain we know it.

Why does this universal problem among speakers happen?

And when can word-finding difficulties indicate something serious?

Everyone will experience an occasional word-finding difficulty, but if they happen very often with a broad range of words, names and numbers, this could be a sign of a neurological disorder.

The steps involved in speaking

Producing spoken words involves several stages of processing.

These include:

• identifying the intended meaning

• selecting the right word from the “mental lexicon” (a mental dictionary of the speaker’s vocabulary)

• retrieving its sound pattern (called its “form”)

• executing the movements of the speech organs for articulating it.

Word-finding difficulties can potentially arise at each of these stages of processing.

When a healthy speaker can’t retrieve a word from their lexicon despite the feeling of knowing it, this is called a “tip-of-the-tongue” phenomenon by language scientists.

Often, the frustrated speaker will try to give a bit of information about their intended word’s meaning, “you know, that thing you hit a nail with”, or its spelling, “it starts with an H!”.

Tip-of-the-tongue states are relatively common and are a type of speech error that occurs primarily during retrieval of the sound pattern of a word (step three above).

What can affect word finding?

Word-finding difficulties occur at all ages but they do happen more often as we get older. In older adults, they can cause frustration and anxiety about the possibility of developing dementia. But they’re not always a cause for concern.

One way researchers investigate word-finding difficulties is to ask people to keep a diary to record how often and in what context they occur. Diary studies have shown that some word types, such as names of people and places, concrete nouns (things, such as “dog” or “building”) and abstract nouns (concepts, such as “beauty” or “truth”), are more likely to result in tip-of-the-tongue states compared with verbs and adjectives.

Less frequently used words are also more likely to result in tip-of-the-tongue states. It’s thought this is because they have weaker connections between their meanings and their sound patterns than more frequently used words.

Laboratory studies have also shown tip-of-the-tongue states are more likely to occur under socially stressful conditions when speakers are told they are being evaluated, regardless of their age. Many people report having experienced tip-of-the-tongue problems during job interviews.

When could it spell more serious issues?

More frequent failures with a broader range of words, names and numbers are likely to indicate more serious issues.

When this happens, language scientists use the terms “anomia” or “anomic aphasia” to describe the condition, which can be associated with brain damage due to stroke, tumours, head injury or dementia such as Alzheimer’s disease.

Recently, the actor Bruce Willis’s family revealed he has been diagnosed with a degenerative disorder known as primary progressive aphasia, for which one of the earliest symptoms is word-finding difficulties rather than memory loss.

Primary progressive aphasia is typically associated with frontotemporal or Alzheimer’s dementias, although it can be associated with other pathologies.

Anomic aphasia can arise due to problems occurring at different stages of speech production. An assessment by a clinical neuropsychologist or speech pathologist can help clarify which processing stage is affected and how serious the problem might be.

For example, if a person is unable to name a picture of a common object such as a hammer, a clinical neuropsychologist or speech pathologist will ask them to describe what the object is used for (the individual might then say “it’s something you hit things with” or “it’s a tool”).

If they can’t, they will be asked to gesture or mime how it’s used. They might also be provided with a cue or prompt, such as the first letter (h) or syllable (ham).

Most people with anomic aphasia benefit greatly from being prompted, indicating they are mostly experiencing problems with later stages of retrieving word forms and motor aspects of speech.

But if they’re unable to describe or mime the object’s use, and cueing does not help, this is likely to indicate an actual loss of word knowledge or meaning. This is typically a sign of a more serious issue such as primary progressive aphasia.

Imaging studies in healthy adults and people with anomic aphasia have shown different areas of the brain are responsible for their word-finding difficulties.

In healthy adults, occasional failures to name a picture of a common object are linked with changes in activity in brain regions that control motor aspects of speech, suggesting a spontaneous problem with articulation rather than a loss of word knowledge.

In anomia due to primary progressive aphasia, brain regions that process word meanings show a loss of nerve cells and connections or atrophy.

Although anomic aphasia is common after strokes to the left hemisphere of the brain, the associated word-finding difficulties do not appear to be distinguishable by specific areas.

There are treatments available for anomic aphasia. These will often involve speech pathologists training the individual on naming tasks using different kinds of cues or prompts to help retrieve words. The cues can be various meaningful features of objects and ideas, or sound features of words, or a combination of both. Smart tablet and phone apps also show promise when used to complement therapy with home-based practice.

The type of cue used for treatment is determined by the nature of the person’s impairment. Successful treatment is associated with changes in activity in brain regions known to support speech production. Unfortunately, there is no effective treatment for primary progressive aphasia, although some studies have suggested speech therapy can produce temporary benefits.

If you’re concerned about your word-finding difficulties or those of a loved one, you can consult your GP for a referral to a clinical neuropsychologist or a speech pathologist.

Greig de Zubicaray, Professor of Neuropsychology, Queensland University of Technology

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Read More........→October 05, 2023